Al2O3-Y2O3-ZrO2/HfO2 materials, and methods of making and using the same

ABSTRACT

Al 2 O 3 —Y 2 O 3 —ZrO 2 /HfO 2  ceramics (including glasses, crystalline ceramics, and glass-ceramics) and methods of making the same. Ceramics according to the present invention can be made, formed as, or converted into glass beads, articles (e.g., plates), fibers, particles, and thin coatings. The particles and fibers are useful, for example, as thermal insulation, filler, or reinforcing material in composites (e.g., ceramic, metal, or polymeric matrix composites). The thin coatings can be useful, for example, as protective coatings in applications involving wear, as well as for thermal management. Certain ceramic particles according to the present invention can be are particularly useful as abrasive particles.

This application is a continuation-in-part of U.S. Ser. No. 09/922,530,filed Aug. 2, 2001 now abandoned, the disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to Al₂O₃—Y₂O₃—ZrO₂/HfO₂ amorphous and/orceramic materials (including glasses, crystalline ceramics, andglass-ceramics) and methods of making the same.

DESCRIPTION OF THE RELATED ART

A large number of amorphous (including glass) and glass-ceramiccompositions are known. The majority of oxide glass systems utilizewell-known glass-formers such as SiO₂, B₂O₃, P₂O₅, GeO₂, TeO₂, As₂O₃,and V₂O₅ to aid in the formation of the glass. Some of the glasscompositions formed with these glass-formers can be heat-treated to formglass-ceramics. The upper use temperature of glasses and glass-ceramicsformed from such glass formers is generally less than 1200° C.,typically about 700-800° C. The glass-ceramics tend to be moretemperature resistant than the glass from which they are formed.

In addition, many properties of known glasses and glass-ceramics arelimited by the intrinsic properties of glass-formers. For example, forSiO₂, B₂O₃, and P₂O₅-based glasses and glass-ceramics, the Young'smodulus, hardness, and strength are limited by such glass-formers. Suchglass and glass-ceramics generally have inferior mechanical propertiesas compared, for example, to Al₂O₃ or ZrO₂. Glass-ceramics having anymechanical properties similar to that of Al₂O₃ or ZrO₂ would bedesirable.

Although some non-conventional glasses such as glasses based on rareearth oxide-aluminum oxide (see, e.g., PCT application havingpublication No. WO 01/27046 A1, published Apr. 19, 2001, and JapaneseDocument No. JP 2000-045129, published Feb. 15, 2000) are known,additional novel glasses and glass-ceramic, as well as use for bothknown and novel glasses and glass-ceramics is desired.

In another aspect, a variety of abrasive particles (e.g., diamondparticles, cubic boron nitride particles, fused abrasive particles, andsintered, ceramic abrasive particles (including sol-gel-derived abrasiveparticles) known in the art. In some abrading applications, the abrasiveparticles are used in loose form, while in others the particles areincorporated into abrasive products (e.g., coated abrasive products,bonded abrasive products, non-woven abrasive products, and abrasivebrushes). Criteria used in selecting abrasive particles used for aparticular abrading application include: abrading life, rate of cut,substrate surface finish, grinding efficiency, and product cost.

From about 1900 to about the mid-1980's, the premier abrasive particlesfor abrading applications such as those utilizing coated and bondedabrasive products were typically fused abrasive particles. There are twogeneral types of fused abrasive particles: (1) fused alpha aluminaabrasive particles (see, e.g., U.S. Pat. No. 1,161,620 (Coulter), U.S.Pat. No. 1,192,709 (Tone), U.S. Pat. No. 1,247,337 (Saunders et al.),U.S. Pat. No. 1,268,533 (Allen), and U.S. Pat. No. 2,424,645 (Baumann etal.)), and (2) fused (sometimes also referred to as “co-fused”)alumina-zirconia abrasive particles (see, e.g., U.S. Pat. No. 3,891,408(Rowse et al.), U.S. Pat. No. 3,781,172 (Pett et al.), U.S. Pat. No.3,893,826 (Quinan et al.), U.S. Pat. No. 4,126,429 (Watson), U.S. Pat.No. 4,457,767 (Poon et al.), and U.S. Pat. No. 5,143,522 (Gibson etal.))(also see, e.g., U.S. Pat. No. 5,023,212 (Dubots et al.), and U.S.Pat. No. 5,336,280 (Dubots et al.), which report the certain fusedoxynitride abrasive particles). Fused alumina abrasive particles aretypically made by charging a furnace with an alumina source such asaluminum ore or bauxite, as well as other desired additives, heating thematerial above its melting point, cooling the melt to provide asolidified mass, crushing the solidified mass into particles, and thenscreening and grading the particles to provide the desired abrasiveparticle size distribution. Fused alumina-zirconia abrasive particlesare typically made in a similar manner, except the furnace is chargedwith both an alumina source and a zirconia source, and the melt is morerapidly cooled than the melt used to make fused alumina abrasiveparticles. For fused alumina-zirconia abrasive particles, the amount ofalumina source is typically about 50-80 percent by weight, and theamount of zirconia, 50-20 percent by weight zirconia. The processes formaking the fused alumina and fused alumina abrasive particles mayinclude removal of impurities from the melt prior to the cooling step.

Although fused alpha alumina abrasive particles and fusedalumina-zirconia abrasive particles are still widely used in abradingapplications (including those utilizing coated and bonded abrasiveproducts, the premier abrasive particles for many abrading applicationssince about the mid-1980's are sol-gel-derived alpha alumina particles(see, e.g., U.S. Pat. No. 4,314,827 (Leitheiser et al.), U.S. Pat. No.4,518,397 (Leitheiser et al.), U.S. Pat. No. 4,623,364 (Cottringer etal.), U.S. Pat. No. 4,744,802 (Schwabel), U.S. Pat. No. 4,770,671(Monroe et al.), U.S. Pat. No. 4,881,951 (Wood et al.), U.S. Pat. No.4,960,441 (Pellow et al.), U.S. Pat. No. 5,139,978 (Wood), U.S. Pat. No.5,201,916 (Berg et al.), U.S. Pat. No. 5,366,523 (Rowenhorst et al.),U.S. Pat. No. 5,429,647 (Larmie), U.S. Pat. No. 5,547,479 (Conwell etal.), U.S. Pat. No. 5,498,269 (Larmie), U.S. Pat. No. 5,551,963(Larmie), and U.S. Pat. No. 5,725,162 (Garg et al.)).

The sol-gel-derived alpha alumina abrasive particles may have amicrostructure made up of very fine alpha alumina crystallites, with orwithout the presence of secondary phases added. The grinding performanceof the sol-gel derived abrasive particles on metal, as measured, forexample, by life of abrasive products made with the abrasive particleswas dramatically longer than such products made from conventional fusedalumina abrasive particles.

Typically, the processes for making sol-gel-derived abrasive particlesare more complicated and expensive than the processes for makingconventional fused abrasive particles. In general, sol-gel-derivedabrasive particles are typically made by preparing a dispersion or solcomprising water, alumina monohydrate (boehmite), and optionallypeptizing agent (e.g., an acid such as nitric acid), gelling thedispersion, drying the gelled dispersion, crushing the dried dispersioninto particles, screening the particles to provide the desired sizedparticles, calcining the particles to remove volatiles, sintering thecalcined particles at a temperature below the melting point of alumina,and screening and grading the particles to provide the desired abrasiveparticle size distribution. Frequently a metal oxide modifier(s) isincorporated into the sintered abrasive particles to alter or otherwisemodify the physical properties and/or microstructure of the sinteredabrasive particles.

There are a variety of abrasive products (also referred to “abrasivearticles”) known in the art. Typically, abrasive products include binderand abrasive particles secured within the abrasive product by thebinder. Examples of abrasive products include: coated abrasive products,bonded abrasive products, nonwoven abrasive products, and abrasivebrushes.

Examples of bonded abrasive products include: grinding wheels, cutoffwheels, and honing stones. The main types of bonding systems used tomake bonded abrasive products are: resinoid, vitrified, and metal.Resinoid bonded abrasives utilize an organic binder system (e.g.,phenolic binder systems) to bond the abrasive particles together to formthe shaped mass (see, e.g., U.S. Pat. No. 4,741,743 (Narayanan et al.),U.S. Pat. No. 4,800,685 (Haynes et al.), U.S. Pat. No. 5,037,453(Narayanan et al.), and U.S. Pat. No. 5,110,332 (Narayanan et al.)).Another major type are vitrified wheels in which a glass binder systemis used to bond the abrasive particles together mass (see, e.g., U.S.Pat. No. 4,543,107 (Rue), U.S. Pat. No. 4,898,587 (Hay et al.), U.S.Pat. No. 4,997,461 (Markhoff-Matheny et al.), and U.S. Pat. No.5,863,308 (Qi et al.)). These glass bonds are usually matured attemperatures between 900° C. to 1300° C. Today vitrified wheels utilizeboth fused alumina and sol-gel-derived abrasive particles. However,fused alumina-zirconia is generally not incorporated into vitrifiedwheels due in part to the thermal stability of alumina-zirconia. At theelevated temperatures at which the glass bonds are matured, the physicalproperties of alumina-zirconia degrade, leading to a significantdecrease in their abrading performance. Metal bonded abrasive productstypically utilize sintered or plated metal to bond the abrasiveparticles.

The abrasive industry continues to desire abrasive particles andabrasive products that are easier to make, cheaper to make, and/orprovide performance advantage(s) over conventional abrasive particlesand products.

SUMMARY OF THE INVENTION

The present invention provides amorphous (including glasses) and/orceramic (including glass, crystalline ceramic, glass-ceramic) materialscomprising (on a theoretical oxide basis; e.g., may be present as areaction product (e.g., Y₃AL₅O₁₂)), Al₂O₃, Y₂O₃, and at least one ofZrO₂ or HfO₂, including glass, crystalline ceramic (e.g., crystallitesof a complex metal oxide(s) (e.g., complex Al₂O₃.Y₂O₃) and/or ZrO₂), andglass-ceramic materials, wherein in amorphous materials not having aT_(g), certain preferred embodiments have x, y, and z dimensions eachperpendicular to each other, and wherein each of the x, y, and zdimensions is at least 5 mm (in some embodiments at least 10 mm), the x,y, and z dimensions is at least 30 micrometers, 35 micrometers, 40micrometers, 45 micrometers, 50 micrometers, 75 micrometers, 100micrometers, 150 micrometers, 200 micrometers, 250 micrometers, 500micrometers, 1000 micrometers, 2000 micrometers, 2500 micrometers, 1 mm,5 mm, or even at least 10 mm. The x, y, and z dimensions of a materialare determined either visually or using microscopy, depending on themagnitude of the dimensions. The reported z dimension is, for example,the diameter of a sphere, the thickness of a coating, or the longestlength of a prismatic shape. Some embodiments of ceramic materialsaccording to the present invention may comprise, for example, less than40 (35, 30, 25, 20, 15, 10, 5, 3, 2, 1, or even zero) percent by weighttraditional glass formers such as SiO₂, As₂O₃, B₂O₃, P₂O₅, GeO₂, TeO₂,V₂O₅, and/or combinations thereof, based on the total weight of theceramic. Ceramics according to the present invention may comprise, forexample, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, 95, or even 100 percent by volume amorphousmaterial. Some embodiments of ceramics according to the presentinvention may comprise, for example, at least 1, 2, 3, 5, 10, 15, 20,25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99,or even 100 percent by volume crystalline ceramic, based on the totalvolume of the ceramic.

Typically, ceramics according to the present invention comprises atleast 30 percent by weight of the Al₂O₃, based on the total weight ofthe ceramic. More typically, ceramics according to the present inventioncomprise at least 30 (desirably, in a range of about 30 to about 60)percent by weight Al₂O₃, at least 20 (about 20 to about 65) percent byweight Y₂O₃, and at least 5 (about 5 to about 30) percent by weight ZrO₂and/or HfO₂, based on the total weight of the ceramic. The weight ratioof ZrO₂:HfO₂ can range of 1:zero (i.e., all ZrO₂; no HfO₂) to zero:1, aswell as, for example, at least about 99, 98, 97, 96, 95, 90, 85, 80, 75,70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 20, 15, 10, and 5 parts (byweight) ZrO₂ and a corresponding amount of HfO₂ (e.g., at least about 99parts (by weight) ZrO₂ and not greater than about 1 part HfO₂) and atleast about 99, 98, 97, 96, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45,40, 35, 30, 25, 20, 20, 15, 10, and 5 parts HfO₂ and a correspondingamount of ZrO₂. Optionally, ceramics according to the present inventionfurther comprise REO.

For ceramics according to the present invention comprising crystallineceramic, some embodiments include those wherein, the ceramic (a)exhibits a microstructure comprising crystallites (e.g., crystallites ofa complex metal oxide(s) (e.g., complex Al₂O₃.Y₂O₃) and/or ZrO₂) havingan average crystallite size of less than 1 micrometer (typically, lessthan 500 nanometers, even less than 300, 200, or 150 nanometers; and insome embodiments, less than 100, 75, 50, 25, or 20 nanometers), and (b)is free of at least one of eutectic microstructure features (i.e., isfree of colonies and lamellar structure) or a non-cellularmicrostructure. It is also within the scope of the present invention forsome embodiments to have at least one crystalline phase within aspecified average crystallite value and at least one (different)crystalline phase outside of a specified average crystallite value.

Some embodiments of the present invention include amorphous materialcomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of theamorphous material collectively comprises the Al₂O₃, Y₂O₃, and at leastone of ZrO₂ or HfO₂, based on the total weight of the amorphousmaterial.

Some embodiments of the present invention include amorphous materialcomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100) percentby weight of the amorphous material collectively comprises the Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, and less than 20 (preferably,less than 15, 10, 5, or even 0) percent by weight SiO₂ and less than 20(preferably, less than 15, 10, 5, or even 0) percent by weight B₂O₃,based on the total weight of the amorphous material.

Some embodiments of the present invention include provides amorphousmaterial comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂,wherein at least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even100) percent by weight of the amorphous material collectively comprisesthe Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, and less than 40(preferably, less than 35, 30, 25, 20, 15, 10, 5, or even 0) percent byweight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight ofthe amorphous material.

Some embodiments of the present invention include ceramic comprisingamorphous material (e.g., at least 5, 10, 15, 20, 25, 30, 35, 40, 45,50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percentby volume amorphous material), the amorphous material comprising Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 80 (85, 90, 95,97, 98, 99, or even 100) percent by weight of the amorphous materialcollectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, based on the total weight of the amorphous material.

Some embodiments of the present invention include ceramic comprisingamorphous material (e.g., at least 5, 10, 15, 20, 25, 30, 35, 40, 45,50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percentby volume amorphous material), the amorphous material comprising Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60 (65, 70, 75,80, 85, 90, 95, 97, 98, 99, or even 100) percent by weight of theamorphous material collectively comprises the Al₂O₃, Y₂O₃, and at leastone of ZrO₂ or HfO₂, and less than 20 (preferably, less than 15, 10, 5,or even 0) percent by weight SiO₂, and less than 20 percent by weightB₂O₃, based on the total weight of the amorphous material. The ceramicmay further comprise crystalline ceramic (e.g., at least 95, 90, 85, 80,75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1percent by volume crystalline ceramic).

Some embodiments of the present invention include ceramic comprisingamorphous material (e.g., at least 5, 10, 15, 20, 25, 30, 35, 40, 45,50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percentby volume amorphous material), the amorphous material comprising Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60 (65, 70, 75,80, 85, 90, 95, 97, 98, 99, or even 100) percent by weight of theamorphous material collectively comprises the Al₂O₃, Y₂O₃, and at leastone of ZrO₂ or HfO₂, and less than 40 percent by weight collectivelySiO₂, B₂O₃, and P₂O₅, based on the total weight of the amorphousmaterial. The ceramic may further comprise crystalline ceramic (e.g., atleast 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20,15, 10, 5, 3, 2, or 1 percent by volume crystalline ceramic).

Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of theglass-ceramic collectively comprises the Al₂O₃, Y₂O₃, and at least oneof ZrO₂ or HfO₂, based on the total weight of the glass-ceramic. Theglass-ceramic may comprise, for example, at least 1, 2, 3, 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95percent by volume glass. The glass-ceramic may comprise, for example, atleast 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35,30, 25, 20, 15, 10, or 5 percent by volume crystalline ceramic.

Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100) percentby weight of the glass-ceramic collectively comprises the Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂, and less than 20 (preferably, lessthan 15, 10, 5, or even 0) percent by weight SiO₂ and less than 20(preferably, less than 15, 10, 5, or even 0) percent by weight B₂O₃,based on the total weight of the glass-ceramic. The glass-ceramic maycomprise, for example, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 percent by volume glass.The glass-ceramic may comprise, for example, at least 99, 98, 97, 95,90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5percent by volume crystalline ceramic.

Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100) percentby weight of the glass-ceramic collectively comprises the Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂, and less than 40 percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass-ceramic. The glass-ceramic may comprise, for example, at least 1,2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, 95, percent by volume amorphous material. The glass-ceramic maycomprise, for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65,60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5 percent by volumecrystalline ceramic.

Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein theglass-ceramic (a) exhibits a microstructure comprising crystallites(e.g., crystallites of a complex metal oxide(s) (e.g., complexAl₂O₃.Y₂O₃) and/or ZrO₂) having an average crystallite size of less than1 micrometer (typically, less than 500 nanometers, or even less than300, 220, or 150 nanometers; and in some embodiments, less than 100, 75,50, 25, or 20 nanometers), and (b) is free of eutectic microstructurefeatures. Some embodiments of the present invention includeglass-ceramic comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂,wherein the glass-ceramic (a) exhibits a non-cellular microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃.Y₂O₃) and/or ZrO₂) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers,even less than 300, 200, or 150 nanometers; and in some embodiments,less than 100, 75, 50, 25, or 20 nanometers). The glass-ceramic maycomprise, for example, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, percent by volume amorphousmaterial. The glass-ceramic may comprise, for example, at least 99, 98,97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15,10, or 5 percent by volume crystalline ceramic. It is also within thescope of the present invention for some embodiments to have at least onecrystalline phase within a specified average crystallite value and atleast one (different) crystalline phase outside of a specified averagecrystallite value.

Some embodiments of the present invention include ceramic comprisingcrystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100percent by volume crystalline ceramic), the crystalline ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 80 (85, 90, 95, 97, 98, 99, or even 100) percent by weight of thecrystalline ceramic collectively comprises the Al₂O₃, Y₂O₃, and at leastone of ZrO₂ or HfO₂, based on the total weight of the crystallineceramic. Some desirable embodiments include those wherein the ceramic(a) exhibits a microstructure comprising crystallites (e.g.,crystallites of a complex metal oxide(s) (e.g., complex Al₂O₃.Y₂O₃)and/or ZrO₂) having an average crystallite size of less than 1micrometer (typically, less than 500 nanometers, or even less than 300,200, or 150 nanometers; and in some embodiments, less than 100, 75, 50,25, or 20 nanometers), and (b) is free of eutectic microstructurefeatures. Some embodiments of the present invention include thosewherein the ceramic (a) exhibits a non-cellular microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃ Y₂O₃) and/or ZrO₂) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers,even less than 300, 200, or 150 nanometers; and in some embodiments,less than 100, 75, 50, 25, or 20 nanometers). The ceramic may comprise,for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55,50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent by volumeamorphous material. It is also within the scope of the present inventionfor some embodiments to have at least one crystalline phase within aspecified average crystallite value and at least one (different)crystalline phase outside of a specified average crystallite value.

Some embodiments of the present invention include ceramic comprisingcrystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100percent by volume crystalline ceramic), the crystalline ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100) percentby volume crystalline ceramic), the crystalline ceramic comprises theAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60 (65,70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100) percent by weight ofthe crystalline ceramic collectively comprises the Al₂O₃.Y₂O₃, and atleast one of ZrO₂ or HfO₂, and less than 20 (preferably, less than 15,10, 5, or even 0) percent by weight SiO₂ and less than 20 (preferably,less than 15, 10, 5, or even 0) percent by weight B₂O₃, based on thetotal weight of the crystalline ceramic. Some desirable embodimentsinclude those wherein the ceramic (a) exhibits a microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃.Y₂O₃) and/or ZrO₂) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers, oreven less than 300, 200, or 150 nanometers; and in some embodiments,less than 100, 75, 50, 25, or 20 nanometers), and (b) is free ofeutectic microstructure features. Some embodiments of the presentinvention include those wherein the ceramic (a) exhibits a non-cellularmicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.Y₂O₃) and/or ZrO₂) having an averagecrystallite size of less than 1 micrometer (typically, less than 500nanometers, even less than 300, 200, or 150 nanometers; and in someembodiments, less than 100, 75, 50, 25, or 20 nanometers). The ceramicmay comprise, for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70,65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent byvolume amorphous material. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified average crystallite value and at least one(different) crystalline phase outside of a specified average crystallitevalue.

Some embodiments of the present invention include ceramic comprisingcrystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100percent by volume crystalline ceramic), the crystalline ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100) percentby weight of the crystalline ceramic collectively comprises the Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, and less than 40 percent byweight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weight ofthe crystalline ceramic. Some desirable embodiments include thosewherein the ceramic (a) exhibits a microstructure comprisingcrystallites (e.g., crystallites of a complex metal oxide(s) (e.g.,complex Al₂O₃.Y₂O₃) and/or ZrO₂) having an average crystallite size ofless than 1 micrometer (typically, less than 500 nanometers, or evenless than less than 300, 200, or 150 nanometers; and in someembodiments, less than 100, 75, 50, 25, or 20 nanometers), and (b) isfree of eutectic microstructure features. Some embodiments of thepresent invention include those wherein the ceramic (a) exhibits anon-cellular microstructure comprising crystallites (e.g., crystallitesof a complex metal oxide(s) (e.g., complex Al₂O₃.Y₂O₃) and/or ZrO₂)having an average crystallite size of less than 1 micrometer (typically,less than 500 nanometers, even less than 300, 200, or 150 nanometers;and in some embodiments, less than 100, 75, 50, 25, or 20 nanometers).The ceramic may comprise, for example, at least 99, 98, 97, 95, 90, 85,80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or1 percent by volume amorphous material. It is also within the scope ofthe present invention for some embodiments to have at least onecrystalline phase within a specified average crystallite value and atleast one (different) crystalline phase outside of a specified averagecrystallite value.

Some embodiments of the present invention include ceramic comprisingcrystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100percent by volume crystalline ceramic), the ceramic comprising Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂. Some desirable embodimentsinclude those wherein the ceramic (a) exhibits a microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃ Y₂O₃) and/or ZrO₂) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers, oreven less than 300, 200, or 150 nanometers; and in some embodiments,less than 100, 75, 50, 25, or 20 nanometers), and (b) is free ofeutectic microstructure features. Some embodiments of the presentinvention include those wherein the ceramic (a) exhibits a non-cellularmicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.Y₂O₃) and/or ZrO₂) having an averagecrystallite size of less than 1 micrometer (typically, less than 500nanometers, even less than 300, 200, or 150 nanometers; and in someembodiments, less than 100, 75, 50, 25, or 20 nanometers). The ceramicmay comprise, for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70,65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent byvolume glass. It is also within the scope of the present invention forsome embodiments to have at least one crystalline phase within aspecified average crystallite value and at least one (different)crystalline phase outside of a specified average crystallite value.

Some embodiments of the present invention include ceramic comprisingcrystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100percent by volume crystalline ceramic), the ceramic comprising Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 80 (85, 90, 95,97, 98, 99, or even 100) percent by weight of the ceramic collectivelycomprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, based onthe total weight of the ceramic. Some desirable embodiments includethose wherein the ceramic (a) exhibits a microstructure comprisingcrystallites (e.g., crystallites of a complex metal oxide(s) (e.g.,complex Al₂O₃.Y₂O₃) and/or ZrO₂) having an average crystallite size ofless than 1 micrometer (typically, less than 500 nanometers, or evenless than 300, 200, or 150 nanometers; and in some embodiments, lessthan 100, 75, 50, 25, or 20 nanometers), and (b) is free of eutecticmicrostructure features. Some embodiments of the present inventioninclude those wherein the ceramic (a) exhibits a non-cellularmicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.Y₂O₃) and/or ZrO₂) having an averagecrystallite size of less than 1 micrometer (typically, less than 500nanometers, even less than 300, 200, or 150 nanometers; and in someembodiments, less than 100, 75, 50, 25, or 20 nanometers). The ceramicmay comprise, for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70,65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent byvolume glass. It is also within the scope of the present invention forsome embodiments to have at least one crystalline phase within aspecified average crystallite value and at least one (different)crystalline phase outside of a specified average crystallite value.

Some embodiments of the present invention include ceramic comprisingcrystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100percent by volume crystalline ceramic), the ceramic comprising Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60 (65, 70, 75,80, 85, 90, 95, 97, 98, 99, or even 100) percent by weight of theceramic collectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂or HfO₂, and less than 20 (preferably, less than 15, 10, 5, or even 0)percent by weight SiO₂ and less than 20 (preferably, less than 15, 10,5, or even 0) percent by weight B₂O₃, based on the total weight of theceramic. Some desirable embodiments include those wherein the ceramic(a) exhibits a microstructure comprising crystallites (e.g.,crystallites of a complex metal oxide(s) (e.g., complex Al₂O₃ Y₂O₃)and/or ZrO₂) having an average crystallite size of less than 1micrometer (typically, less than 500 nanometers, or even less than 300,200, or 150 nanometers; and in some embodiments, less than 100, 75, 50,25, or 20 nanometers), and (b) is free of eutectic microstructurefeatures. Some embodiments of the present invention include thosewherein the ceramic (a) exhibits a non-cellular microstructurecomprising crystallites (e.g., crystallites of a complex metal oxide(s)(e.g., complex Al₂O₃.Y₂O₃) and/or ZrO₂) having an average crystallitesize of less than 1 micrometer (typically, less than 500 nanometers,even less than 300, 200, or 150 nanometers; and in some embodiments,less than 100, 75, 50, 25, or 20 nanometers). The ceramic may comprise,for example, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55,50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent by volumeglass. It is also within the scope of the present invention for someembodiments to have at least one crystalline phase within a specifiedaverage crystallite value and at least one (different) crystalline phaseoutside of a specified average crystallite value.

Some embodiments of the present invention include ceramic comprisingcrystalline ceramic (e.g., at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100percent by volume crystalline ceramic), the ceramic comprising Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60 (65, 70, 75,80, 85, 90, 95, 97, 98, 99, or even 100) percent by weight of theceramic collectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂or HfO₂, and less than 40 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the ceramic. Some desirableembodiments include those wherein the ceramic (a) exhibits amicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃ Y₂O₃) and/or ZrO₂) having an averagecrystallite size of less than 1 micrometer (typically, less than 500nanometers, or even less than 300, 200, or 150 nanometers; and in someembodiments, less than 100, 75, 50, 25, or 20 nanometers), and (b) isfree of eutectic microstructure features. Some embodiments of thepresent invention include those wherein the ceramic (a) exhibits anon-cellular microstructure comprising crystallites (e.g., crystallitesof a complex metal oxide(s) (e.g., complex Al₂O₃.Y₂O₃) and/or ZrO₂)having an average crystallite size of less than 1 micrometer (typically,less than 500 nanometers, even less than 300, 200, or 150 nanometers;and in some embodiments, less than 100, 75, 50, 25, or 20 nanometers).The ceramic may comprise, for example, at least 99, 98, 97, 95, 90, 85,80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, 5, 3, 2, or1 percent by volume glass. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified average crystallite value and at least one(different) crystalline phase outside of a specified average crystallitevalue.

Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein theglass-ceramic (a) exhibits a microstructure comprising crystallites(e.g., crystallites of a complex metal oxide(s) (e.g., complexAl₂O₃.Y₂O₃) and/or ZrO₂) having an average crystallite size of less than200 nanometers (150 nanometers, 100 nanometers, 75 nanometers, or even50 nanometers) and (b) has a density of at least 90% (95%, 96%, 97%,98%, 99%, 99.5%, or 100%) of theoretical density. Some embodiments canbe free of at least one of eutectic microstructure features or anon-cellular microstructure. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified average crystallite value and at least one(different) crystalline phase outside of a specified average crystallitevalue.

Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, herein theglass-ceramic (a) exhibits a microstructure comprising crystallites(e.g., crystallites of a complex metal oxide(s) (e.g., complexAl₂O₃.Y₂O₃) and/or ZrO₂), wherein none of the crystallites are greaterthan 200 nanometers (150 nanometers, 100 nanometers, 75 nanometers, oreven 50 nanometers) in size and (b) has a density of at least 90% (95%,96%, 97%, 98%, 99%, 99.5%, or 100%) of theoretical density. Someembodiments can be free of at least one of eutectic microstructurefeatures or a non-cellular microstructure. It is also within the scopeof the present invention for some embodiments to have at least onecrystalline phase within a specified crystallite value and at least one(different) crystalline phase outside of a specified crystallite value.

Some embodiments of the present invention include glass-ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein theglass-ceramic (a) exhibits a microstructure comprising crystallites(e.g., crystallites of a complex metal oxide(s) (e.g., complexAl₂O₃.Y₂O₃) and/or ZrO₂), wherein at least a portion of the crystallitesare not greater than 150 nanometers (100 nanometers, 75 nanometers, oreven 50 nanometers) in size and (b) has a density of at least 90% (95%,96%, 97%, 98%, 99%, 99.5%, or 100%) of theoretical density. Someembodiments can be free of at least one of eutectic microstructurefeatures or a non-cellular microstructure. It is also within the scopeof the present invention for some embodiments to have at least onecrystalline phase within a specified crystallite value and at least one(different) crystalline phase outside of a specified crystallite value.

Some embodiments of the present invention include fully crystallizedglass-ceramic comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂wherein the glass-ceramic (a) exhibits a microstructure comprisingcrystallites (e.g., crystallites of a complex metal oxide(s) (e.g.,complex Al₂O₃.Y₂O₃) and/or ZrO₂) having an average crystallite size notgreater than 1 micrometer (500 nanometers, 300 nanometers, 200nanometers, 150 nanometers, 100 nanometers, 75 nanometers, or even 50nanometers) in size and (b) has a density of at least 90% (95%, 96%,97%, 98%, 99%, 99.5%, or 100%) of theoretical density. Some embodimentscan be free of at least one of eutectic microstructure features or anon-cellular microstructure. It is also within the scope of the presentinvention for some embodiments to have at least one crystalline phasewithin a specified average crystallite value and at least one(different) crystalline phase outside of a specified average crystallitevalue.

For ceramics according to the present invention comprising crystallineceramic, some embodiments include those wherein the ceramic (a) exhibitsa microstructure comprising crystallites (e.g., crystallites of acomplex metal oxide(s) (e.g., complex Al₂O₃.Y₂O₃) and/or ZrO₂) having anaverage crystallite size of less than 200 nanometers (150 nanometers,100 nanometers, 75 nanometers, or even 50 nanometers) and (b) has adensity of at least 90% (95%, 96%, 97%, 98%, 99%, 99.5%, or 100%) oftheoretical density. Some embodiments can be free of at least one ofeutectic microstructure features or a non-cellular microstructure. It isalso within the scope of the present invention for some embodiments tohave at least one crystalline phase within a specified averagecrystallite value and at least one (different) crystalline phase outsideof a specified average crystallite value.

For ceramics according to the present invention comprising crystallineceramic, some embodiments include those comprising Al₂O₃, Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein the ceramic (a) exhibits amicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃ Y₂O₃) and/or ZrO₂), wherein none ofthe crystallites are greater than 200 nanometers (150 nanometers, 100nanometers, 75 nanometers, or even 50 nanometers) in size and (b) has adensity of at least 90% (95%, 96%, 97%, 98%, 99%, 99.5%, or 100%) oftheoretical density. Some embodiments can be free of at least one ofeutectic microstructure features or a non-cellular microstructure. It isalso within the scope of the present invention for some embodiments tohave at least one crystalline phase within a specified crystallite valueand at least one (different) crystalline phase outside of a specifiedcrystallite value.

For ceramics according to the present invention comprising crystallineceramic, some embodiments include those comprising Al₂O₃, Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein the ceramic (a) exhibits amicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.Y₂O₃) and/or ZrO₂), wherein at leasta portion of the crystallites are not greater than 150 nanometers (100nanometers, 75 nanometers, or even 50 nanometers) in size and (b) has adensity of at least 90% (95%, 96%, 97%, 98%, 99%, 99.5%, or 100%) oftheoretical density. Some embodiments can be free of at least one ofeutectic microstructure features or a non-cellular microstructure. It isalso within the scope of the present invention for some embodiments tohave at least one crystalline phase within a specified crystallite valueand at least one (different) crystalline phase outside of a specifiedcrystallite value.

For ceramics according to the present invention comprising crystallineceramic, some embodiments include those comprising Al₂O₃, Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein the ceramic (a) exhibits amicrostructure comprising crystallites (e.g., crystallites of a complexmetal oxide(s) (e.g., complex Al₂O₃.Y₂O₃) and/or ZrO₂) having an averagecrystallite size not greater than 1 micrometer (500 nanometers, 300nanometers, 200 nanometers, 150 nanometers, 100 nanometers, 75nanometers, or even 50 nanometers) in size and (b) has a density of atleast 90% (95%, 96%, 97%, 98%, 99%, 99.5%, or 100%) of theoreticaldensity. Some embodiments can be free of at least one of eutecticmicrostructure features or a non-cellular microstructure. It is alsowithin the scope of the present invention for some embodiments to haveat least one crystalline phase within a specified crystallite value andat least one (different) crystalline phase outside of a specifiedaverage value.

Some embodiments of the present invention include a glass-ceramiccomprising alpha Al₂O₃, crystalline ZrO₂, and a first complexAl₂O₃.Y₂O₃, wherein at least one of the alpha Al₂O₃, the crystallineZrO₂, or the first complex Al₂O₃.Y₂O₃ has an average crystal size notgreater than 200 nanometers (in some embodiments preferably, not greaterthan 75 nanometers, or even not greater than 50 nanometers), and whereinthe abrasive particles have a density of at least 90 (in someembodiments at least 95, 96, 97, 98, 99, 99.5, or even 100) percent oftheoretical density. In some embodiments, preferably at least 75 (80,85, 90, 95, 97, or even at least 99) percent by number of the crystalsizes are not greater than 200 nanometers. In some embodimentspreferably, the glass-ceramic further comprises a second, differentcomplex Al₂O₃.Y₂O₃. In some embodiments preferably, the glass-ceramicfurther comprises a complex Al₂O₃.REO.

Some embodiments of the present invention a glass-ceramic comprising afirst complex Al₂O₃.Y₂O₃, a second, different complex Al₂O₃.Y₂O₃, andcrystalline ZrO₂, wherein for at least one of the first complexAl₂O₃.Y₂O₃, the second complex Al₂O₃.Y₂O₃, or the crystalline ZrO₂, atleast 90 (in some embodiments preferably, 95, or even 100) percent bynumber of the crystal sizes thereof are not greater than 200 nanometers(in some embodiments preferably, not greater than 100 nanometers, notgreater than 75 nanometers, or even not greater than 50 nanometers), andwherein the abrasive particles have a density of at least 90 (in someembodiments at least 95, 96, 97, 98, 99, 99.5, or even 100) percent oftheoretical density. In some embodiments preferably, the glass-ceramicfurther comprises a second, different complex Al₂O₃.Y₂O₃. In someembodiments preferably, the glass-ceramic particles further comprises acomplex Al₂O₃.REO.

Some embodiments of the present invention include a glass-ceramiccomprising a first complex Al₂O₃.Y₂O₃, a second, different complexAl₂O₃.Y₂O₃, and crystalline ZrO₂, wherein at least one of the firstcomplex Al₂O₃.Y₂O₃, the second, different complex Al₂O₃.Y₂O₃, or thecrystalline ZrO₂ has an average crystal size not greater than 100nanometers (in some embodiments preferably, not greater than 75nanometers, or even not greater than 50 nanometers), and wherein theabrasive particles have a density of at least 90 (in some embodiments atleast 95, 96, 97, 98, 99, 99.5, or even 100) percent of theoreticaldensity. In some embodiments, preferably at least 75 (80, 85, 90, 95,97, or even at least 99) percent by number of the crystal sizes are notgreater than 200 nanometers. In some embodiments preferably, theglass-ceramic further comprises a second, different complex Al₂O₃.Y₂O₃.In some embodiments preferably, the glass-ceramic further comprises acomplex Al₂O₃.REO.

Some embodiments of the present invention include a glass-ceramiccomprising a first complex Al₂O₃.Y₂O₃, a second, different complexAl₂O₃.Y₂O₃, and crystalline ZrO₂, wherein for at least one of the firstcomplex Al₂O₃.Y₂O₃, the second, different complex Al₂O₃.Y₂O₃, or thecrystalline ZrO₂, at least 90 (in some embodiments preferably, 95, oreven 100) percent by number of the crystal sizes thereof are not greaterthan 200 nanometers (in some embodiments preferably, not greater than100 nanometers, not greater 75 nanometers, or even not greater 50nanometers), and wherein the abrasive particles have a density of atleast 90 (in some embodiments at least 95, 96, 97, 98, 99, 99.5, or even100) percent of theoretical density. In some embodiments preferably, theglass-ceramic further comprises a complex Al₂O₃.REO.

In another aspect, the present invention provides methods for makingceramics according to the present invention. For example, the presentinvention provides a method for making ceramic according to the presentinvention comprising material (e.g., glass, or glass and crystallineceramic(including glass-ceramic)), the method comprising:

-   -   melting sources of at least Al₂O₃, Y₂O₃, and at least one of        ZrO₂ or HfO₂ to provide a melt; and    -   cooling the melt to provide ceramic comprising material.        It is also within the scope of the present invention to        heat-treat certain amorphous material or ceramics comprising        amorphous material described herein to a ceramic comprising        crystalline ceramic (including glass-ceramic) (i.e., such that        at least a portion of the amorphous material is converted to a        glass-ceramic).

In this application:

“amorphous material” refers to material derived from a melt and/or avapor phase that lacks any long range crystal structure as determined byX-ray diffraction and/or has an exothermic peak corresponding to thecrystallization of the amorphous material as determined by a DTA(differential thermal analysis) as determined by the test describedherein entitled “Differential Thermal Analysis”;

“ceramic” includes glass, crystalline ceramic, glass-ceramic, andcombinations thereof;

“complex metal oxide” refers to a metal oxide comprising two or moredifferent metal elements and oxygen (e.g., CeAl₁₁O₁₈, Dy₃Al₅O₁₂,MgAl₂O₄, and Y₃Al₅O₁₂);

“complex Al₂O₃.metal oxide” refers to a complex metal oxide comprising,on a theoretical oxide basis, Al₂O₃ and one or more metal elements otherthan Al (e.g., CeAl₁₁O₁₈, Dy₃Al₅O₁₂, MgAl₂O₄, and Y₃Al₅O₁₂);

“complex Al₂O₃.Y₂O₃” refers to a complex metal oxide comprising, on atheoretical oxide basis, Al₂O₃ and Y₂O₃ (e.g., Y₃Al₅O₁₂);

“complex Al₂O₃.REO” refers to a complex metal oxide comprising, on atheoretical oxide basis, Al₂O₃ and rare earth oxide (e.g., CeAl₁₁O₁₈ andDy₃Al₅O₁₂);

“glass” refers to amorphous material exhibiting a glass transitiontemperature;

“glass-ceramic” refers to ceramics comprising crystals formed byheat-treating amorphous material;

“T_(g)” refers to the glass transition temperature as determined by thetest described herein entitled “Differential Thermal Analysis”;

“T_(x)” refers to the crystallization temperature as determined by thetest described herein entitled “Differential Thermal Analysis”;

“rare earth oxides” refers to cerium oxide (e.g.,CeO₂), dysprosium oxide(e.g., Dy₂O₃), erbium oxide (e.g., Er₂O₃), europium oxide (e.g., Eu₂O₃),gadolinium (e.g., Gd₂O₃), holmium oxide (e.g., Ho₂O₃), lanthanum oxide(e.g., La₂O₃), lutetium oxide (e.g., Lu₂O₃), neodymium oxide (e.g.,Nd₂O₃), praseodymium oxide (e.g., Pr₆O₁₁), samarium oxide (e.g., Sm₂O₃),terbium (e.g., Tb₂O₃), thorium oxide (e.g., Th₄O₇), thulium (e.g.,Tm₂O₃), and ytterbium oxide (e.g., Yb₂O₃), and combinations thereof;

“REO” refers to rare earth oxide(s).

Further, it is understood herein that unless it is stated that a metaloxide (e.g., Al₂O₃, complex Al₂O₃.metal oxide, etc.) is crystalline, forexample, in a glass-ceramic, it may be amorphous, crystalline, orportions amorphous and portions crystalline. For example if aglass-ceramic comprises Al₂O₃ and ZrO₂, the Al₂O₃ and ZrO₂ may each bein an amorphous state, crystalline state, or portions in an amorphousstate and portions in a crystalline state, or even as a reaction productwith another metal oxide(s) (e.g., unless it is stated that, forexample, Al₂O₃ is present as crystalline Al₂O₃ or a specific crystallinephase of Al₂O₃ (e.g., alpha Al₂O₃), it may be present as crystallineAl₂O₃ and/or as part of one or more crystalline complex Al₂O₃.metaloxides.

Further, it is understood that glass-ceramics formed by heatingamorphous material not exhibiting a T_(g) may not actually compriseglass, but rather may comprise the crystals and amorphous material thatdoes not exhibiting a T_(g).

Ceramics articles according to the present invention can be made, formedas, or converted into glass beads (e.g., beads having diameters of atleast 1 micrometers, 5 micrometers, 10 micrometers, 25 micrometers, 50micrometers, 100 micrometers, 150 micrometers, 250 micrometers, 500micrometers, 750 micrometers, 1 mm, 5 mm, or even at least 10 mm),plates, fibers, particles, and coatings (e.g., thin coatings). The glassbeads can be useful, for example, in reflective devices such asretroreflective sheeting, alphanumeric plates, and pavement markings.The particles and fibers are useful, for example, as thermal insulation,filler, or reinforcing material in composites (e.g., ceramic, metal, orpolymeric matrix composites). The thin coatings can be useful, forexample, as protective coatings in applications involving wear, as wellas for thermal management. Examples of articles according of the presentinvention include kitchenware (e.g., plates), dental brackets, andreinforcing fibers, cutting tool inserts, abrasive materials, andstructural components of gas engines, (e.g., valves and bearings). Otherarticles include those having a protective coating of ceramic on theouter surface of a body or other substrate. Certain ceramic particlesaccording to the present invention can be particularly useful asabrasive particles. The abrasive particles can be incorporated into anabrasive article, or used in loose form.

Abrasive articles according to the present invention comprise binder anda plurality of abrasive particles, wherein at least a portion of theabrasive particles are the abrasive particles according to the presentinvention. Exemplary abrasive products include coated abrasive articles,bonded abrasive articles (e.g., wheels), non-woven abrasive articles,and abrasive brushes. Coated abrasive articles typically comprise abacking having first and second, opposed major surfaces, and wherein thebinder and the plurality of abrasive particles form an abrasive layer onat least a portion of the first major surface.

In some embodiments, preferably, at least 5, 10, 15, 20, 25, 30, 35, 40,45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100 percent byweight of the abrasive particles in an abrasive article are the abrasiveparticles according to the present invention, based on the total weightof the abrasive particles in the abrasive article.

Abrasive particles are usually graded to a given particle sizedistribution before use. Such distributions typically have a range ofparticle sizes, from coarse particles fine particles. In the abrasiveart this range is sometimes referred to as a “coarse”, “control” and“fine” fractions. Abrasive particles graded according to industryaccepted grading standards specify the particle size distribution foreach nominal grade within numerical limits. Such industry acceptedgrading standards (i.e., specified nominal grades) include those knownas the American National Standards Institute, Inc. (ANSI) standards,Federation of European Producers of Abrasive Products (FEPA) standards,and Japanese Industrial Standard (JIS) standards. In one aspect, thepresent invention provides a plurality of abrasive particles having aspecified nominal grade, wherein at least a portion of the plurality ofabrasive particles are abrasive particles according to the presentinvention. In some embodiments, preferably, at least 5, 10, 15, 20, 25,30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, or even 100percent by weight of the plurality of abrasive particles are theabrasive particles according to the present invention, based on thetotal weight of the plurality of abrasive particles.

The present invention also provides a method of abrading a surface, themethod comprising:

contacting abrasive particles according to the present invention with asurface of a workpiece; and

moving at least one of the abrasive particles according to the presentinvention or the contacted surface to abrade at least a portion of thesurface with at least one of the abrasive particles according to thepresent invention.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a SEM photomicrograph of polished cross-sections ofheat-treated Example 1 material;

FIG. 2 is a DTA curve of Example 1 material;

FIG. 3 is a fragmentary cross-sectional schematic view of a coatedabrasive article including abrasive particles according to the presentinvention;

FIG. 4 is a perspective view of a bonded abrasive article includingabrasive particles according to the present invention; and

FIG. 5 is an enlarged schematic view of a nonwoven abrasive articleincluding abrasive particles according to the present invention;

DETAILED DESCRIPTION

In general, ceramics according to the present invention can be made byheating (including in a flame) the appropriate metal oxide sources toform a melt, desirably a homogenous melt, and then rapidly cooling themelt to provide amorphous materials or ceramic comprising amorphousmaterials. Amorphous materials and ceramics comprising amorphousmaterials according to the present invention can be made, for example,by heating (including in a flame) the appropriate metal oxide sources toform a melt, desirably a homogenous melt, and then rapidly cooling themelt to provide amorphous material. Some embodiments of amorphousmaterials can be made, for example, by melting the metal oxide sourcesin any suitable furnace (e.g., an inductive heated furnace, a gas-firedfurnace, or an electrical furnace), or, for example, in a plasma. Theresulting melt is cooled (e.g., discharging the melt into a coolingmedia (e.g., high velocity air jets, liquids, metal plates (includingchilled metal plates), metal rolls (including chilled metal rolls),metal balls (including chilled metal balls), and the like)).

In one method, amorphous materials and ceramic comprising amorphousmaterials according to the present invention can be made utilizing flamefusion as disclosed, for example, in U.S. Pat. No. 6,254,981 (Castle),the disclosure of which is incorporated herein by reference. In thismethod, the metal oxide sources materials are fed (e.g., in the form ofparticles, sometimes referred to as “feed particles”) directly into aburner (e.g., a methane-air burner, an acetylene-oxygen burner, ahydrogen-oxygen burner, and like), and then quenched, for example, inwater, cooling oil, air, or the like. Feed particles can be formed, forexample, by grinding, agglomerating (e.g., spray-drying), melting, orsintering the metal oxide sources. The size of feed particles fed intothe flame generally determine the size of the resulting amorphousmaterial comprising particles.

Some embodiments of amorphous materials can also be obtained by othertechniques, such as: laser spin melt with free fall cooling, Taylor wiretechnique, plasmatron technique, hammer and anvil technique, centrifugalquenching, air gun splat cooling, single roller and twin rollerquenching, roller-plate quenching and pendant drop melt extraction (see,e.g., Rapid Solidification of Ceramics, Brockway et. al, Metals AndCeramics Information Center, A Department of Defense InformationAnalysis Center, Columbus, Ohio, January, 1984, the disclosure of whichis incorporated here as a reference). Some embodiments of amorphousmaterials may also be obtained by other techniques, such as: thermal(including flame or laser or plasma-assisted) pyrolysis of suitableprecursors, physical vapor synthesis (PVS) of metal precursors andmechanochemical processing.

Useful Al₂O₃—Y₂O₃—ZrO₂/HfO₂ formulations include those at or near aeutectic composition(s) (e.g., ternary eutectic compositions). Inaddition to Al₂O₃—Y₂O₃—ZrO₂/HfO₂ compositions disclosed herein, othersuch compositions, including quaternary and other higher order eutecticcompositions, may be apparent to those skilled in the art afterreviewing the present disclosure.

Sources, including commercial sources, of (on a theoretical oxide basis)Al₂O₃ include bauxite (including both natural occurring bauxite andsynthetically produced bauxite), calcined bauxite, hydrated aluminas(e.g., boehmite, and gibbsite), aluminum, Bayer process alumina,aluminum ore, gamma alumina, alpha alumina, aluminum salts, aluminumnitrates, and combinations thereof. The Al₂O₃ source may contain, oronly provide, Al₂O₃. Alternatively, the Al₂O₃ source may contain, orprovide Al₂O₃, as well as one or more metal oxides other than Al₂O₃(including materials of or containing complex Al₂O₃.metal oxides (e.g.,Dy₃Al₅O₁₂, Y₃Al₅O₁₂, CeAl₁₁O₁₈, etc.)).

Sources, including commercial sources, of (on a theoretical oxide basis)Y₂O₃ include yttrium oxide powders, yttrium, yttrium-containing ores,and yttrium salts (e.g., yttrium carbonates, nitrates, chlorides,hydroxides, and combinations thereof). The Y₂O₃ source may contain, oronly provide, Y₂O₃. Alternatively, the Y₂O₃ source may contain, orprovide Y₂O₃, as well as one or more metal oxides other than Y₂O₃(including materials of or containing complex Y₂O₃ metal oxides (e.g.,Y₃Al₅O₁₂)).

Sources, including commercial sources, of (on a theoretical oxide basis)ZrO₂ include zirconium oxide powders, zircon sand, zirconium,zirconium-containing ores, and zirconium salts (e.g., zirconiumcarbonates, acetates, nitrates, chlorides, hydroxides, and combinationsthereof). In addition, or alternatively, the ZrO₂ source may contain, orprovide ZrO₂, as well as other metal oxides such as hafnia. Sources,including commercial sources, of (on a theoretical oxide basis) HfO₂include hafnium oxide powders, hafnium, hafnium-containing ores, andhafnium salts. In addition, or alternatively, the HfO₂ source maycontain, or provide HfO₂, as well as other metal oxides such as ZrO₂.

Optionally, ceramics according to the present invention further compriseother oxide metal oxides (i.e., metal oxides other than Al₂O₃, rareearth oxide(s), and ZrO₂/HfO₂). Other useful metal oxide may alsoinclude, on a theoretical oxide basis, BaO, CaO, Cr₂O₃, CoO, Fe₂O₃,GeO₂, Li₂O, MgO, MnO, NiO, Na₂O, Sc₂O₃, SrO, TiO₂, ZnO, and combinationsthereof. Sources, including commercial sources, include the oxidesthemselves, complex oxides, ores, carbonates, acetates, nitrates,chlorides, hydroxides, etc. These metal oxides are added to modify aphysical property of the resulting ceramic and/or improve processing.These metal oxides are typically are added anywhere from 0 to 50% byweight, in some embodiments preferably 0 to 25% by weight and morepreferably 0 to 50% by weight of the ceramic material depending, forexample, upon the desired property.

In some embodiments, it may be advantageous for at least a portion of ametal oxide source (in some embodiments, preferably, 10 15, 20, 25, 30,35, 40, 45, or even 50, percent by weight) to be obtained by addingparticulate, metallic material comprising at least one of a metal (e.g.,Al, Ca, Cu, Cr, Fe, Li, Mg, Ni, Ag, Ti, Zr, and combinations thereof),M, that has a negative enthalpy of oxide formation or an alloy thereofto the melt, or otherwise metal them with the other raw materials.Although not wanting to be bound by theory, it is believed that the heatresulting from the exothermic reaction associated with the oxidation ofthe metal is beneficial in the formation of a homogeneous melt andresulting amorphous material. For example, it is believed that theadditional heat generated by the oxidation reaction within the rawmaterial eliminates or minimizes insufficient heat transfer, and hencefacilitates formation and homogeneity of the melt, particularly whenforming amorphous particles with x, y, and z dimensions over 150micrometers. It is also believed that the availability of the additionalheat aids in driving various chemical reactions and physical processes(e.g., densification, and spherodization) to completion. Further, it isbelieved for some embodiments, the presence of the additional heatgenerated by the oxidation reaction actually enables the formation of amelt, which otherwise is difficult or otherwise not practical due tohigh melting point of the materials. Further, the presence of theadditional heat generated by the oxidation reaction actually enables theformation of amorphous material that otherwise could not be made, orcould not be made in the desired size range. Another advantage of theinvention include, in forming the amorphous materials, that many of thechemical and physical processes such as melting, densification andspherodizing can be achieved in a short time, so that very high quenchrates be can achieved. For additional details, see copending applicationhaving U.S. Ser. No. 10/211,639, filed the same date as the instantapplication, the disclosure of which is incorporated herein byreference.

The addition of certain metal oxides may alter the properties and/orcrystalline structure or microstructure of ceramics according to thepresent invention, as well as the processing of the raw materials andintermediates in making the ceramic. For example, oxide additions suchas MgO, CaO, Li₂O, and Na₂O have been observed to alter both the T_(g)and T_(x) (wherein T_(x) is the crystallization temperature) of glass.Although not wishing to be bound by theory, it is believed that suchadditions influence glass formation. Further, for example, such oxideadditions may decrease the melting temperature of the overall system(i.e., drive the system toward lower melting eutectic), and ease ofglass-formation. Complex eutectics in multi component systems(quaternary, etc.) may result in better glass-forming ability. Theviscosity of the liquid melt and viscosity of the glass in its “working”range may also be affected by the addition of metal oxides other thanAl₂O₃, Y₂O₃, and ZrO₂/HfO₂ (such as MgO, CaO, Li₂O, and Na₂O).

Typically, amorphous materials and the glass-ceramics according to thepresent invention have x, y, and z dimensions each perpendicular to eachother, and wherein each of the x, y, and z dimensions is at least 10micrometers. In some embodiments, the x, y, and z dimensions is at least30 micrometers, 35 micrometers, 40 micrometers, 45 micrometers, 50micrometers, 75 micrometers, 100 micrometers, 150 micrometers, 200micrometers, 250 micrometers, 500 micrometers, 1000 micrometers, 2000micrometers, 2500 micrometers, 1 mm, 5 mm, or even at least 10 mm. Thex, y, and z dimensions of a material are determined either visually orusing microscopy, depending on the magnitude of the dimensions. Thereported z dimension is, for example, the diameter of a sphere, thethickness of a coating, or the longest length of a prismatic shape.Crystallization of amorphous material and ceramic comprising theamorphous material to form glass-ceramics may also be affected by theadditions of materials. For example, certain metals, metal oxides (e.g.,titanates and zirconates), and fluorides, for example, may act asnucleation agents resulting in beneficial heterogeneous nucleation ofcrystals. Also, addition of some oxides may change nature of metastablephases devitrifying from the glass upon reheating. In another aspect,for ceramics according to the present invention comprising crystallineZrO₂, it may be desirable to add metal oxides (e.g., TiO₂, CaO, and MgO)that are known to stabilize tetragonal/cubic form of ZrO₂.Y₂O₃ is alsoknown to stabilize tetragonal/cubic form of ZrO₂.

The particular selection of metal oxide sources and other additives formaking ceramics according to the present invention typically takes intoaccount, for example, the desired composition and microstructure of theresulting crystalline containing ceramics, the desired degree ofcrystallinity, if any, the desired physical properties (e.g., hardnessor toughness) of the resulting ceramics, avoiding or minimizing thepresence of undesirable impurities, the desired characteristics of theresulting ceramics, and/or the particular process (including equipmentand any purification of the raw materials before and/or during fusionand/or solidification) being used to prepare the ceramics.

In some instances, it may be preferred to incorporate limited amounts ofmetal oxides selected from the group consisting of: Na₂O, P₂O₅, SiO₂,TeO₂, V₂O₃, and combinations thereof. Sources, including commercialsources, include the oxides themselves, complex oxides, ores,carbonates, acetates, nitrates, chlorides, hydroxides, etc. These metaloxides may be added, for example, to modify a physical property of theresulting abrasive particles and/or improve processing. These metaloxides when used are typically are added from greater than 0 to 20% byweight, preferably greater than 0 to 5% by weight and more preferablygreater than 0 to 2% by weight of the glass-ceramic depending, forexample, upon the desired property.

The metal oxide sources and other additives can be in any form suitableto the process and equipment being used to make ceramics according tothe present invention. The raw materials can be melted and quenchedusing techniques and equipment known in the art for making oxide glassesand amorphous metals. Desirable cooling rates include those of 50K/s andgreater. Cooling techniques known in the art include roll-chilling.Roll-chilling can be carried out, for example, by melting the metaloxide sources at a temperature typically 20-200° C. higher than themelting point, and cooling/quenching the melt by spraying it under highpressure (e.g., using a gas such as air, argon, nitrogen or the like)onto a high-speed rotary roll(s). Typically, the rolls are made of metaland are water cooled. Metal book molds may also be useful forcooling/quenching the melt.

Other techniques for forming melts, cooling/quenching melts, and/orotherwise forming glass include vapor phase quenching, plasma spraying,melt-extraction, and gas or centrifugal atomization. Vapor phasequenching can be carried out, for example, by sputtering, wherein themetal alloys or metal oxide sources are formed into a sputteringtarget(s) which are used. The target is fixed at a predeterminedposition in a sputtering apparatus, and a substrate(s) to be coated isplaced at a position opposing the target(s). Typical pressures of 10⁻³torr of oxygen gas and Ar gas, discharge is generated between thetarget(s) and a substrate(s), and Ar or oxygen ions collide against thetarget to start reaction sputtering, thereby depositing a film ofcomposition on the substrate. For additional details regarding plasmaspraying, see, for example, copending application having U.S. Ser. No.10/211,640, filed the same date as the instant application, thedisclosure of which is incorporated herein by reference.

Gas atomization involves melting feed particles to convert them to melt.A thin stream of such melt is atomized through contact with a disruptiveair jet (i.e., the stream is divided into fine droplets). The resultingsubstantially discrete, generally ellipsoidal glass particles (e.g.,beads) are then recovered. Examples of bead sizes include those having adiameter in a range of about 5 micrometers to about 3 mm.Melt-extraction can be carried out, for example, as disclosed in U.S.Pat. No. 5,605,870 (Strom-Olsen et al.), the disclosure of which isincorporated herein by reference. Containerless glass forming techniquesutilizing laser beam heating as disclosed, for example, in PCTapplication having Publication No. WO 01/27046 Al, published Apr. 4,2001, the disclosure of which is incorporated herein by reference, mayalso be useful in making glass according to the present invention.

The cooling rate is believed to affect the properties of the quenchedamorphous material. For instance, glass transition temperature, densityand other properties of glass typically change with cooling rates.

Rapid cooling may also be conducted under controlled atmospheres, suchas a reducing, neutral, or oxidizing environment to maintain and/orinfluence the desired oxidation states, etc. during cooling. Theatmosphere can also influence glass formation by influencingcrystallization kinetics from undercooled liquid. For example, largerundercooling of Al₂O₃ melts without crystallization has been reported inargon atmosphere as compared to that in air.

The microstructure or phase composition (glassy/amorphous/crystalline)of a material can be determined in a number of ways. Various informationcan be obtained using optical microscopy, electron microscopy,differential thermal analysis (DTA), and x-ray diffraction (XRD), forexample.

Using optical microscopy, amorphous material is typically predominantlytransparent due to the lack of light scattering centers such as crystalboundaries, while crystalline material shows a crystalline structure andis opaque due to light scattering effects.

A percent amorphous yield can be calculated for beads using a −100+120mesh size fraction (i.e., the fraction collected between 150-micrometeropening size and 125-micrometer opening size screens). The measurementsare done in the following manner. A single layer of beads is spread outupon a glass slide. The beads are observed using an optical microscope.Using the crosshairs in the optical microscope eyepiece as a guide,beads that lay along a straight line are counted either amorphous orcrystalline depending on their optical clarity. A total of 500 beads arecounted and a percent amorphous yield is determined by the amount ofamorphous beads divided by total beads counted.

Using DTA, the material is classified as amorphous if the correspondingDTA trace of the material contains an exothermic crystallization event(T_(x)). If the same trace also contains an endothermic event (T_(g)) ata temperature lower than T_(x) it is considered to consist of a glassphase. If the DTA trace of the material contains no such events, it isconsidered to contain crystalline phases.

Differential thermal analysis (DTA) can be conducted using the followingmethod. DTA runs can be made (using an instrument such as that obtainedfrom Netzsch Instruments, Selb, Germany under the trade designation“NETZSCH STA 409 DTA/TGA”) using a −140+170 mesh size fraction (i.e.,the fraction collected between 105-micrometer opening size and90-micrometer opening size screens). An amount of each screened sample(typically about 400 milligrams (mg)) is placed in a 100-microliterAl₂O₃ sample holder. Each sample is heated in static air at a rate of10° C./minute from room temperature (about 25° C.) to 1100° C.

Using powder x-ray diffraction, XRD, (using an x-ray diffractometer suchas that obtained under the trade designation “PHILLIPS XRG 3100” fromPhillips, Mahwah, N.J., with copper K α1 radiation of 1.54050 Angstrom)the phases present in a material can be determined by comparing thepeaks present in the XRD trace of the crystallized material to XRDpatterns of crystalline phases provided in JCPDS (Joint Committee onPowder Diffraction Standards) databases, published by InternationalCenter for Diffraction Data. Furthermore, an XRD can be usedqualitatively to determine types of phases. The presence of a broaddiffused intensity peak is taken as an indication of the amorphousnature of a material. The existence of both a broad peak andwell-defined peaks is taken as an indication of existence of crystallinematter within an amorphous matrix. The initially formed amorphousmaterial or ceramic (including glass prior to crystallization) may belarger in size than that desired. The amorphous material or ceramic canbe converted into smaller pieces using crushing and/or comminutingtechniques known in the art, including roll crushing, canary milling,jaw crushing, hammer milling, ball milling, jet milling, impactcrushing, and the like. In some instances, it is desired to have two ormultiple crushing steps. For example, after the ceramic is formed(solidified), it may be in the form of larger than desired. The firstcrushing step may involve crushing these relatively large masses or“chunks” to form smaller pieces. This crushing of these chunks may beaccomplished with a hammer mill, impact crusher or jaw crusher. Thesesmaller pieces may then be subsequently crushed to produce the desiredparticle size distribution. In order to produce the desired particlesize distribution (sometimes referred to as grit size or grade), it maybe necessary to perform multiple crushing steps. In general the crushingconditions are optimized to achieve the desired particle shape(s) andparticle size distribution. Resulting particles that are of the desiredsize may be recrushed if they are too large, or “recycled” and used as araw material for re-melting if they are too small.

The shape of particles can depend, for example, on the compositionand/or microstructure of the ceramic, the geometry in which it wascooled, and the manner in which the ceramic is crushed (i.e., thecrushing technique used). In general, where a “blocky” shape ispreferred, more energy may be employed to achieve this shape.Conversely, where a “sharp” shape is preferred, less energy may beemployed to achieve this shape. The crushing technique may also bechanged to achieve different desired shapes. For some abrasive particlean average aspect ratio ranging from 1:1 to 5:1 is typically desired,and in some embodiments 1.25:1 to 3:1, or even 1.5:1 to 2.5:1.

It is also within the scope of the present invention, for example, todirectly form articles in desired shapes. For example, desired articlesmay be formed (including molded) by pouring or forming the melt into amold.

Surprisingly, it was found that ceramics of present invention could beobtained without limitations in dimensions. This was found to bepossible through a coalescing step performed at temperatures above glasstransition temperature. This coalescing step in essence forms a largersized body from two or more smaller particles. For instance, as evidentfrom FIG. 2, glass of present invention undergoes glass transition(T_(g)) before significant crystallization occurs (T_(x)) as evidencedby the existence of endotherm (T_(g)) at lower temperature than exotherm(T_(x)). For example, ceramic (including glass prior tocrystallization), may also be provided by heating, for example,particles comprising the amorphous material, and/or fibers, etc. abovethe T_(g) such that the particles, etc. coalesce to form a shape andcooling the coalesced shape. The temperature and pressure used forcoalescing may depend, for example, upon composition of the amorphousmaterial and the desired density of the resulting material. Thetemperature should below glass crystallization temperature, and forglasses, greater than the glass transition temperature. In certainembodiments, the heating is conducted at at least one temperature in arange of about 850° C. to about 1100° C. (in some embodiments,preferably 900° C. to 1000° C.). Typically, the amorphous material isunder pressure (e.g., greater than zero to 1 GPa or more) duringcoalescence to aid the coalescence of the amorphous material. In oneembodiment, a charge of the particles, etc. is placed into a die andhot-pressing is performed at temperatures above glass transition whereviscous flow of glass leads to coalescence into a relatively large part.Examples of typical coalescing techniques include hot pressing, hotisostatic pressure, hot extrusion and the like. For example, amorphousmaterial comprising particles (obtained, for example, by crushing)(including beads and microspheres), fibers, etc. may formed into alarger particle size. Typically, it is generally preferred to cool theresulting coalesced body before further heat treatment. After heattreatment if so desired, the coalesced body may be crushed to smallerparticle sizes or a desired particle size distribution.

It is also within the scope of the present invention to conductadditional heat-treatment to further improve desirable properties of thematerial. For example, hot-isostatic pressing may be conducted (e.g., attemperatures from about 900° C. to about 1400° C.) to remove residualporosity, increasing the density of the material. Optionally, theresulting, coalesced article can be heat-treated to provideglass-ceramic, crystalline ceramic, or ceramic otherwise comprisingcrystalline ceramic.

Coalescing of the amorphous material and/or glass-ceramic (e.g.,particles) may also be accomplished by a variety of methods, includingpressureless or pressure sintering (e.g., sintering, plasma assistedsintering, hot pressing, HIPing, hot forging, hot extrusion, etc.).

Heat-treatment can be carried out in any of a variety of ways, includingthose known in the art for heat-treating glass to provideglass-ceramics. For example, heat-treatment can be conducted in batches,for example, using resistive, inductively or gas heated furnaces.Alternatively, for example, heat-treatment can be conductedcontinuously, for example, using rotary kilns. In the case of a rotarykiln, the material is fed directly into a kiln operating at the elevatedtemperature. The time at the elevated temperature may range from a fewseconds (in some embodiments even less than 5 seconds) to a few minutesto several hours. The temperature may range anywhere from 900° C. to1600° C., typically between 1200° C. to 1500° C. It is also within thescope of the present invention to perform some of the heat-treatment inbatches (e.g., for the nucleation step) and another continuously (e.g.,for the crystal growth step and to achieve the desired density). For thenucleation step, the temperature typically ranges between about 900° C.to about 1100° C., in some embodiments, preferably in a range from about925° C. to about 1050° C. Likewise for the density step, the temperaturetypically is in a range from about 1100° C. to about 1600° C., in someembodiments, preferably in a range from about 1200° C. to about 1500° C.This heat treatment may occur, for example, by feeding the materialdirectly into a furnace at the elevated temperature. Alternatively, forexample, the material may be feed into a furnace at a much lowertemperature (e.g., room temperature) and then heated to desiredtemperature at a predetermined heating rate. It is within the scope ofthe present invention to conduct heat-treatment in an atmosphere otherthan air. In some cases it might be even desirable to heat-treat in areducing atmosphere(s). Also, for, example, it may be desirable toheat-treat under gas pressure as in, for example, hot-isostatic press,or in gas pressure furnace. It is within the scope of the presentinvention to convert (e.g., crush) the resulting article or heat-treatedarticle to provide particles (e.g., abrasive particles).

The amorphous material is heat-treated to at least partially crystallizethe amorphous material to provide glass-ceramic. The heat-treatment ofcertain glasses to form glass-ceramics is well known in the art. Theheating conditions to nucleate and grow glass-ceramics are known for avariety of glasses. Alternatively, one skilled in the art can determinethe appropriate conditions from a Time-Temperature-Transformation (TTT)study of the glass using techniques known in the art. One skilled in theart, after reading the disclosure of the present invention should beable to provide TTT curves for glasses according to the presentinvention, determine the appropriate nucleation and/or crystal growthconditions to provide glass-ceramics according to the present invention.

Typically, glass-ceramics are stronger than the amorphous materials fromwhich they are formed. Hence, the strength of the material may beadjusted, for example, by the degree to which the amorphous material isconverted to crystalline ceramic phase(s). Alternatively, or inaddition, the strength of the material may also be affected, forexample, by the number of nucleation sites created, which may in turn beused to affect the number, and in turn the size of the crystals of thecrystalline phase(s). For additional details regarding formingglass-ceramics, see, for example Glass-Ceramics, P. W. McMillan,Academic Press, Inc., 2^(nd) edition, 1979, the disclosure of which isincorporated herein by reference.

For example, during heat-treatment of some exemplary amorphous materialsfor making glass-ceramics according to present invention, formation ofphases such as La₂Zr₂O₇, and, if ZrO₂ is present, cubic/tetragonal ZrO₂,in some cases monoclinic ZrO₂, have been observed at temperatures aboveabout 900° C. Although not wanting to be bound by theory, it is believedthat zirconia-related phases are the first phases to nucleate from theamorphous material. Formation of Al₂O₃, ReAlO₃ (wherein Re is at leastone rare earth cation), ReAl₁₁O₁₈, Re₃Al₅O₁₂, Y₃Al₅O₁₂, etc. phases arebelieved to generally occur at temperatures above about 925° C.Typically, crystallite size during this nucleation step is on order ofnanometers. For example, crystals as small as 10-15 nanometers have beenobserved. For at least some embodiments, heat-treatment at about 1300°C. for about 1 hour provides a full crystallization. In generally,heat-treatment times for each of the nucleation and crystal growth stepsmay range of a few seconds (in some embodiments even less than 5seconds) to several minutes to an hour or more.

Examples of crystalline phases which may be present in ceramicsaccording to the present invention include: complex Al₂O₃.metal oxide(s)(e.g., complex Al₂O₃.REO (e.g., ReAlO₃ (e.g., GdAlO₃ LaAlO₃), ReAl₁₁O₁₈(e.g., LaAl₁₁O₁₈,), and Re₃Al₅O₁₂ (e.g., Dy₃Al₅O₁₂)), complex Al₂O₃.Y₂O₃(e.g., Y₃Al₅O₁₂), and complex ZrO₂.REO (e.g., La₂Zr₂O₇)), Al₂O₃ (e.g.,α-Al₂O₃), and ZrO₂ (e.g., cubic ZrO₂ and tetragonal ZrO₂).

It is also with in the scope of the present invention to substitute aportion of the yttrium and/or aluminum cations in a complex Al₂O₃.metaloxide (e.g., complex Al₂O₃.Y₂O₃ (e.g., yttrium aluminate exhibiting agarnet crystal structure)) with other cations. For example, a portion ofthe Al cations in a complex Al₂O₃.Y₂O₃ may be substituted with at leastone cation of an element selected from the group consisting of: Cr, Ti,Sc, Fe, Mg, Ca, Si, Co, and combinations thereof. For example, a portionof the Y cations in a complex Al₂O₃.Y₂O₃ may be substituted with atleast one cation of an element selected from the group consisting of:Ce, Dy, Er, Eu, Gd, Ho, La, Lu, Nd, Pr, Sm, Th, Tm, Yb, Fe, Ti, Mn, V,Cr, Co, Ni, Cu, Mg, Ca, Sr, and combinations thereof. Similarly, it isalso with in the scope of the present invention to substitute a portionof the aluminum cations in alumina. For example, Cr, Ti, Sc, Fe, Mg, Ca,Si, and Co can substitute for aluminum in the alumina. The substitutionof cations as described above may affect the properties (e.g. hardness,toughness, strength, thermal conductivity, etc.) of the fused material.

It is also with in the scope of the present invention to substitute aportion of the rare earth and/or aluminum cations in a complexAl₂O₃.metal oxide (e.g., complex Al₂O₃.REO) with other cations. Forexample, a portion of the Al cations in a complex Al₂O₃.REO may besubstituted with at least one cation of an element selected from thegroup consisting of: Cr, Ti, Sc, Fe, Mg, Ca, Si, Co, and combinationsthereof. For example, a portion of the Y cations in a complex Al₂O₃.REOmay be substituted with at least one cation of an element selected fromthe group consisting of: Y, Fe, Ti, Mn, V, Cr, Co, Ni, Cu, Mg, Ca, Sr,and combinations thereof. Similarly, it is also with in the scope of thepresent invention to substitute a portion of the aluminum cations inalumina. For example, Cr, Ti, Sc, Fe, Mg, Ca, Si, and Co can substitutefor aluminum in the alumina. The substitution of cations as describedabove may affect the properties (e.g. hardness, toughness, strength,thermal conductivity, etc.) of the fused material.

The average crystal size can be determined by the line intercept methodaccording to the ASTM standard E 112-96 “Standard Test Methods forDetermining Average Grain Size”. The sample is mounted in mounting resin(such as that obtained under the trade designation “TRANSOPTIC POWDER”from Buehler, Lake Bluff, Ill.) typically in a cylinder of resin about2.5 cm in diameter and about 1.9 cm high. The mounted section isprepared using conventional polishing techniques using a polisher (suchas that obtained from Buehler, Lake Bluff, Ill. under the tradedesignation “ECOMET 3”). The sample is polished for about 3 minutes witha diamond wheel, followed by 5 minutes of polishing with each of 45, 30,15, 9, 3, and 1-micrometer slurries. The mounted and polished sample issputtered with a thin layer of gold-palladium and viewed using ascanning electron microscopy (such as the JEOL SEM Model JSM 840A). Atypical back-scattered electron (BSE) micrograph of the microstructurefound in the sample is used to determine the average crystal size asfollows. The number of crystals that intersect per unit length (N_(L))of a random straight line drawn across the micrograph are counted. Theaverage crystal size is determined from this number using the followingequation.

${{Average}\mspace{14mu}{Crystal}\mspace{14mu}{Size}} = \frac{1.5}{N_{L}M}$

Where N_(L) is the number of crystals intersected per unit length and Mis the magnification of the micrograph. In another aspect, ceramics(including glass-ceramics) according to the present invention maycomprise at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55,60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent byvolume crystallites, wherein the crystallites have an average size ofless than 1 micrometer. In another aspect, ceramics (includingglass-ceramics) according to the present invention may comprise lessthan at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60,65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent by volumecrystallites, wherein the crystallites have an average size of less than0.5 micrometer. In another aspect, ceramics (including glass-ceramics)according to the present invention may comprise less than at least 1, 2,3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, 95, 97, 98, 99, or even 100 percent by volume crystallites, whereinthe crystallites have an average size of less than 0.3 micrometer. Inanother aspect, ceramics (including glass-ceramics) according to thepresent invention may comprise less than at least 1, 2, 3, 5, 10, 15,20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98,99, or even 100 percent by volume crystallites, wherein the crystalliteshave an average size of less than 0.15 micrometer.

Crystalline phases that may be present in ceramics according to thepresent invention include alumina (e.g., alpha and transition aluminas),Y₂O₃, HfO₂, ZrO₂, as well as, for example, one or more other metaloxides such as BaO, CaO, Cr₂O₃, CoO, Fe₂O₃, GeO₂, Li₂O, MgO, MnO, NiO,Na₂O, P₂O₅, REO, Sc₂O₃, SiO₂, SrO, TeO₂, TiO₂, V₂O₃, ZnO, “complex metaloxides” (including “complex Al₂O₃ metal oxide (e.g., complex Al₂O₃Y₂O₃)), and combinations thereof.

Some embodiments of the present invention also include glass comprisingAl₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂,wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100) percent byweight of the glass collectively comprises the Al₂O₃, at least one ofREO or Y₂O₃, and at least one of ZrO₂ or HfO₂, based on the total weightof the glass.

Some embodiments of the present invention also include glass comprisingAl₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂,wherein at least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even100) percent by weight of the glass collectively comprises the Al₂O₃, atleast one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, and lessthan 20 (preferably, less than 15, 10, 5, or even 0) percent by weightSiO₂ and less than 20 (preferably, less than 15, 10, 5, or even 0)percent by weight B₂O₃, based on the total weight of the glass.

Some embodiments of the present invention also include provides glasscomprising Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, oreven 100) percent by weight of the glass collectively comprises theAl₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂,and less than 40 (preferably, less than 35, 30, 25, 20, 15, 10, 5, oreven 0) percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based onthe total weight of the glass.

Some embodiments of the present invention also include ceramiccomprising glass (e.g., at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50,55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent byvolume glass), the glass comprising Al₂O₃, at least one of REO or Y₂O₃,and at least one of ZrO₂ or HfO₂, wherein at least 80 (85, 90, 95, 97,98, 99, or even 100) percent by weight of the glass collectivelycomprises the Al₂O₃, at least one of REO or Y₂O₃, and at least one ofZrO₂ or HfO₂, based on the total weight of the glass.

Some embodiments of the present invention also include ceramiccomprising glass (e.g., at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50,55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent byvolume glass), the glass comprising Al₂O₃, at least one of REO or Y₂O₃,and at least one of ZrO₂ or HfO₂, wherein at least 60 (65, 70, 75, 80,85, 90, 95, 97, 98, 99, or even 100) percent by weight of the glasscollectively comprises the Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, and less than 20 (preferably, less than 15,10, 5, or even 0) percent by weight SiO₂ and less than 20 (preferably,less than 15, 10, 5, or even 0) percent by weight B₂O₃, based on thetotal weight of the glass. The ceramic may further comprise crystallineceramic (e.g., at least 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40,35, 30, 25, 20, 15, 10, 5, 3, 2, or 1 percent by volume crystallineceramic).

Some embodiments of the present invention also include ceramiccomprising glass (e.g., at least 5, 10, 15, 20, 25, 30, 35, 40, 45, 50,55, 60, 65, 70, 75, 80, 85, 90, 95, 97, 98, 99, or even 100 percent byvolume glass), the glass comprising Al₂O₃, at least one of REO or Y₂O₃,and at least one of ZrO₂ or HfO₂, wherein at least 60 (65, 70, 75, 80,85, 90, 95, 97, 98, 99, or even 100) percent by weight of the glasscollectively comprises the Al₂O₃, at least one of REO or Y₂O₃, and atleast one of ZrO₂ or HfO₂, and less than 40 percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass. The ceramic may further comprise crystalline ceramic (e.g., atleast 95, 90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20,15, 10, 5, 3, 2, or 1 percent by volume crystalline ceramic).

Some embodiments of the present invention also include glass-ceramiccomprising Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 80 (85, 90, 95, 97, 98, 99, or even 100)percent by weight of the glass-ceramic collectively comprises the Al₂O₃,at least one of REO or Y₂O₃, and at least one of ZrO₂ or HfO₂, based onthe total weight of the glass-ceramic. The glass-ceramic may comprise,for example, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50,55, 60, 65, 70, 75, 80, 85, 90, or 95 percent by volume glass. Theglass-ceramic may comprise, for example, at least 99, 98, 97, 95, 90,85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5percent by volume crystalline ceramic.

Some embodiments of the present invention also include glass-ceramiccomprising Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, oreven 100) percent by weight of the glass-ceramic collectively comprisesthe Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂ orHfO₂, and less than 20 (preferably, less than 15, 10, 5, or even 0)percent by weight SiO₂ and less than 20 (preferably, less than 15, 10,5, or even 0) percent by weight B₂O₃, based on the total weight of theglass-ceramic. The glass-ceramic may comprise, for example, at least 1,2, 3, 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85,90, or 95 percent by volume glass. The glass-ceramic may comprise, forexample, at least 99, 98, 97, 95, 90, 85, 80, 75, 70, 65, 60, 55, 50,45, 40, 35, 30, 25, 20, 15, 10, or 5 percent by volume crystallineceramic.

Some embodiments of the present invention also include glass-ceramiccomprising Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 (65, 70, 75, 80, 85, 90, 95, 97, 98, 99, oreven 100) percent by weight of the glass-ceramic collectively comprisesthe Al₂O₃, at least one of REO or Y₂O₃, and at least one of ZrO₂ orHfO₂, and less than 40 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass-ceramic. The glass-ceramicmay comprise, for example, at least 1, 2, 3, 5, 10, 15, 20, 25, 30, 35,40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, percent by volume glass.The glass-ceramic may comprise, for example, at least 99, 98, 97, 95,90, 85, 80, 75, 70, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, 10, or 5percent by volume crystalline ceramic.

Additional details regarding ceramics comprising Al₂O₃, REO, and atleast one of ZrO₂ or HfO₂, including making, using, and properties, canbe found in application having U.S. Ser. Nos. 09/922,526, 09/922,527,and 09/922,526, filed Aug. 2, 2001, and U.S. Ser. Nos. 10/211,630;10/211,639; 10/211,034; 10/211,044; 10/211,628; 10/211,640; and10/211,684, filed the same date as the instant application, thedisclosures of which are incorporated herein by reference.

Crystals formed by heat-treating amorphous to provide embodiments ofglass-ceramics according to the present invention may be, for example,equiaxed, columnar, or flattened splat-like features.

Although an amorphous material, glass-ceramic, etc. according to thepresent invention may be in the form of a bulk material, it is alsowithin the scope of the present invention to provide compositescomprising an amorphous material, glass-ceramic, etc. according to thepresent invention. Such a composite may comprise, for example, a phaseor fibers (continuous or discontinuous) or particles (includingwhiskers) (e.g., metal oxide particles, boride particles, carbideparticles, nitride particles, diamond particles, metallic particles,glass particles, and combinations thereof) dispersed in an amorphousmaterial, glass-ceramic, etc. according to the present invention,invention or a layered-composite structure (e.g., a gradient ofglass-ceramic to amorphous material used to make the glass-ceramicand/or layers of different compositions of glass-ceramics).

Certain glasses according to the present invention may have, forexample, a T_(g) in a range of about 810° C. to about 890° C.

The average hardness of the material of the present invention can bedetermined as follows. Sections of the material are mounted in mountingresin (obtained under the trade designation “TRANSOPTIC POWDER” fromBuehler, Lake Bluff, Ill.) typically in a cylinder of resin about 2.5 cmin diameter and about 1.9 cm high. The mounted section is prepared usingconventional polishing techniques using a polisher (such as thatobtained from Buehler, Lake Bluff, Ill. under the trade designation“ECOMET 3”). The sample is polished for about 3 minutes with a diamondwheel, followed by 5 minutes of polishing with each of 45, 30, 15, 9, 3,and 1-micrometer slurries. The microhardness measurements are made usinga conventional microhardness tester (such as that obtained under thetrade designation “MITUTOYO MVK-VL” from Mitutoyo Corporation, Tokyo,Japan) fitted with a Vickers indenter using a 100-gram indent load. Themicrohardness measurements are made according to the guidelines statedin ASTM Test Method E384 Test Methods for Microhardness of Materials(1991), the disclosure of which is incorporated herein by reference.

Certain glasses according to the present invention may have, forexample, an average hardness of at least 5 GPa (more desirably, at least6 GPa, 7 GPa, 8 GPa, or 9 GPa; typically in a range of about 5 GPa toabout 10 GPa), crystalline ceramics according to the present inventionat least 5 GPa (more desirably, at least 6 GPa, 7 GPa, 8 GPa, 9 GPa, 10GPa, 11 GPa, 12 GPa, 13 GPa, 14 GPa, 15 GPa, 16 GPa, 17 GPa, or 18 GPa(or more); typically in a range of about 2 GPa to about 18 GPa), andglass-ceramics according to the present invention or ceramics accordingto the present invention comprising glass and crystalline ceramic atleast 5 GPa (more desirably, at least 6 GPa, 7 GPa, 8 GPa, 9 GPa, 10GPa, 11 GPa, 12 GPa, 13 GPa, 14 GPa, 15 GPa, 16 GPa, 17 GPa, 18 GPa, or19 GPa; typically in a range of about 5 GPa to about 18 GPa). Abrasiveparticles according to the present invention have an average hardness ofat least 15 GPa, in some embodiments, preferably, at least 16 GPa, atleast 17 GPa, or even at least 18 GPa.

Typically, and desirably, the (true) density, sometimes referred to asspecific gravity, of ceramic according to the present invention istypically at least 70% of theoretical density. More desirably, the(true) density of ceramic according to the present invention is at least75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 99.5% or 100% oftheoretical density. Abrasive particles according to the presentinvention have densities of at least 85%, 90%, 92%, 95%, 96%, 97%, 98%,99%, 99.5% or even 100% of theoretical density.

Articles can be made using ceramics according to the present invention,for example, as a filler, reinforcement material, and/or matrixmaterial. For example, ceramic according to the present invention can bein the form of particles and/or fibers suitable for use as reinforcingmaterials in composites (e.g., ceramic, metal, or polymeric(thermosetting or thermoplastic)). The particles and/or fibers may, forexample, increase the modulus, heat resistance, wear resistance, and/orstrength of the matrix material. Although the size, shape, and amount ofthe particles and/or fibers used to make a composite may depend, forexample, on the particular matrix material and use of the composite, thesize of the reinforcing particles typically range about 0.1 to 1500micrometers, more typically 1 to 500 micrometers, and desirably between2 to 100 micrometers. The amount of particles for polymeric applicationsis typically about 0.5 percent to about 75 percent by weight, moretypically about 1 to about 50 percent by weight. Examples ofthermosetting polymers include: phenolic, melamine, urea formaldehyde,acrylate, epoxy, urethane polymers, and the like. Examples ofthermoplastic polymers include: nylon, polyethylene, polypropylene,polyurethane, polyester, polyamides, and the like.

Examples of uses for reinforced polymeric materials (i.e., reinforcingparticles according to the present invention dispersed in a polymer)include protective coatings, for example, for concrete, furniture,floors, roadways, wood, wood-like materials, ceramics, and the like, aswell as, anti-skid coatings and injection molded plastic parts andcomponents.

Further, for example, ceramic according to the present invention can beused as a matrix material. For example, ceramics according to thepresent invention can be used as a binder for ceramic materials and thelike such as diamond, cubic-BN, Al₂O₃, ZrO₂, Si₃N₄, and SiC. Examples ofuseful articles comprising such materials include composite substratecoatings, cutting tool inserts abrasive agglomerates, and bondedabrasive articles such as vitrified wheels. The use of ceramicsaccording to the present invention can be used as binders may, forexample, increase the modulus, heat resistance, wear resistance, and/orstrength of the composite article.

Abrasive particles according to the present invention generally comprisecrystalline ceramic (e.g., at least 75, 80, 85, 90, 91, 92, 93, 94, 95,96, 97, 98, 99, 99.5, or even 100 percent by volume) crystallineceramic. In another aspect, the present invention provides a pluralityof particles having a particle size distribution ranging from fine tocoarse, wherein at least a portion of the plurality of particles areabrasive particles according to the present invention. In anotheraspect, embodiments of abrasive particles according to the presentinvention generally comprise (e.g., at least 75, 80, 85, 90, 91, 92, 93,94, 95, 96, 97, 98, 99, 99.5, or even 100 percent by volume)glass-ceramic according to the present invention.

Abrasive particles according to the present invention can be screenedand graded using techniques well known in the art, including the use ofindustry recognized grading standards such as ANSI (American NationalStandard Institute), FEPA (Federation Europeenne des Fabricants deProducts Abrasifs), and JIS (Japanese Industrial Standard). Abrasiveparticles according to the present invention may be used in a wide rangeof particle sizes, typically ranging in size from about 0.1 to about5000 micrometers, more typically from about 1 to about 2000 micrometers;desirably from about 5 to about 1500 micrometers, more desirably fromabout 100 to about 1500 micrometers.

In a given particle size distribution, there will be a range of particlesizes, from coarse particles fine particles. In the abrasive art thisrange is sometimes referred to as a “coarse”, “control” and “fine”fractions. Abrasive particles graded according to industry acceptedgrading standards specify the particle size distribution for eachnominal grade within numerical limits. Such industry accepted gradingstandards include those known as the American National StandardsInstitute, Inc. (ANSI) standards, Federation of European

Producers of Abrasive Products (FEPA) standards, and Japanese IndustrialStandard (JIS) standards. ANSI grade designations (i.e., specifiednominal grades) include: ANSI 4, ANSI 6, ANSI 8, ANSI 16, ANSI 24, ANSI36, ANSI 40, ANSI 50, ANSI 60, ANSI 80, ANSI 100, ANSI 120, ANSI 150,ANSI 180, ANSI 220, ANSI 240, ANSI 280, ANSI 320, ANSI 360, ANSI 400,and ANSI 600. Preferred ANSI grades comprising abrasive particlesaccording to the present invention are ANSI 8-220. FEPA gradedesignations include P8, P12, P16, P24, P36, P40, P50, P60, P80, P100,P120, P150, P180, P220, P320, P400, P500, P600, P800, P1000, P1200.Preferred FEPA grades comprising abrasive particles according to thepresent invention are P12-P220. JIS grade designations include JIS8, JIS12, JIS 16, JIS524, JIS36, JIS46, JIS54, JIS60, JIS80, JIS 100, JIS 150,JIS 180, JIS220, JIS240, J280, JIS320, JIS360, JIS400, JIS600, JIS800,JIS 1000, JIS 1500, JIS2500, JIS4000, JIS6000, JIS8000, and JIS 10,000.Preferred JIS grades comprising abrasive particles according to thepresent invention are JIS8-220.

After crushing and screening, there will typically be a multitude ofdifferent abrasive particle size distributions or grades. Thesemultitudes of grades may not match a manufacturer's or supplier's needsat that particular time. To minimize inventory, it is possible torecycle the off demand grades back into melt to form glass. Thisrecycling may occur after the crushing step, where the particles are inlarge chunks or smaller pieces (sometimes referred to as “fines”) thathave not been screened to a particular distribution.

In another aspect, the present invention provides a method for makingabrasive particles, the method comprising heat-treating glass particlesor glass-containing particles according to the present invention toprovide abrasive particles comprising a glass-ceramic according to thepresent invention. Alternatively, for example, the present inventionprovides a method for making abrasive particles, the method comprisingheat-treating glass according to the present invention, and crushing theresulting heat-treated material to provide abrasive particles comprisinga glass-ceramic according to the present invention. When crushed, glasstends to provide sharper particles than crushing significantlycrystallized glass-ceramics or crystalline material.

In another aspect, the present invention provides agglomerate abrasivegrains each comprising a plurality of abrasive particles according tothe present invention bonded together via a binder. In another aspect,the present invention provides an abrasive article (e.g., coatedabrasive articles, bonded abrasive articles (including vitrified,resinoid, and metal bonded grinding wheels, cutoff wheels, mountedpoints, and honing stones), nonwoven abrasive articles, and abrasivebrushes) comprising a binder and a plurality of abrasive particles,wherein at least a portion of the abrasive particles are abrasiveparticles (including where the abrasive particles are agglomerated)according to the present invention. Methods of making such abrasivearticles and using abrasive articles are well known to those skilled inthe art. Furthermore, abrasive particles according to the presentinvention can be used in abrasive applications that utilize abrasiveparticles, such as slurries of abrading compounds (e.g., polishingcompounds), milling media, shot blast media, vibratory mill media, andthe like.

Coated abrasive articles generally include a backing, abrasiveparticles, and at least one binder to hold the abrasive particles ontothe backing. The backing can be any suitable material, including cloth,polymeric film, fibre, nonwoven webs, paper, combinations thereof, andtreated versions thereof. The binder can be any suitable binder,including an inorganic or organic binder (including thermally curableresins and radiation curable resins). The abrasive particles can bepresent in one layer or in two layers of the coated abrasive article.

An example of a coated abrasive article is depicted in FIG. 3. Referringto this figure, coated abrasive article 1 has a backing (substrate) 2and abrasive layer 3. Abrasive layer 3 includes abrasive particlesaccording to the present invention 4 secured to a major surface ofbacking 2 by make coat 5 and size coat 6. In some instances, a supersizecoat (not shown) is used.

Bonded abrasive articles typically include a shaped mass of abrasiveparticles held together by an organic, metallic, or vitrified binder.Such shaped mass can be, for example, in the form of a wheel, such as agrinding wheel or cutoff wheel. The diameter of grinding wheelstypically is about 1 cm to over 1 meter; the diameter of cut off wheelsabout 1 cm to over 80 cm (more typically 3 cm to about 50 cm). The cutoff wheel thickness is typically about 0.5 mm to about 5 cm, moretypically about 0.5 mm to about 2 cm. The shaped mass can also be in theform, for example, of a honing stone, segment, mounted point, disc (e.g.double disc grinder) or other conventional bonded abrasive shape. Bondedabrasive articles typically comprise about 3-50% by volume bondmaterial, about 30-90% by volume abrasive particles (or abrasiveparticle blends), up to 50% by volume additives (including grindingaids), and up to 70% by volume pores, based on the total volume of thebonded abrasive article.

A preferred form is a grinding wheel. Referring to FIG. 4, grindingwheel 10 is depicted, which includes abrasive particles according to thepresent invention 11, molded in a wheel and mounted on hub 12.

Nonwoven abrasive articles typically include an open porous loftypolymer filament structure having abrasive particles according to thepresent invention distributed throughout the structure and adherentlybonded therein by an organic binder. Examples of filaments includepolyester fibers, polyamide fibers, and polyaramid fibers. In FIG. 5, aschematic depiction, enlarged about 100×, of a typical nonwoven abrasivearticle is provided. Such a nonwoven abrasive article comprises fibrousmat 50 as a substrate, onto which abrasive particles according to thepresent invention 52 are adhered by binder 54.

Useful abrasive brushes include those having a plurality of bristlesunitary with a backing (see, e.g., U.S. Pat. No. 5,427,595 (Pihl etal.), U.S. Pat. No. 5,443,906 (Pihl et al.), U.S. Pat. No. 5,679,067(Johnson et al.), and U.S. Pat. No. 5,903,951 (Ionta et al.), thedisclosure of which is incorporated herein by reference). Desirably,such brushes are made by injection molding a mixture of polymer andabrasive particles.

Suitable organic binders for making abrasive articles includethermosetting organic polymers. Examples of suitable thermosettingorganic polymers include phenolic resins, urea-formaldehyde resins,melamine-formaldehyde resins, urethane resins, acrylate resins,polyester resins, aminoplast resins having pendant α,β-unsaturatedcarbonyl groups, epoxy resins, acrylated urethane, acrylated epoxies,and combinations thereof. The binder and/or abrasive article may alsoinclude additives such as fibers, lubricants, wetting agents,thixotropic materials, surfactants, pigments, dyes, antistatic agents(e.g., carbon black, vanadium oxide, graphite, etc.), coupling agents(e.g., silanes, titanates, zircoaluminates, etc.), plasticizers,suspending agents, and the like. The amounts of these optional additivesare selected to provide the desired properties. The coupling agents canimprove adhesion to the abrasive particles and/or filler. The binderchemistry may thermally cured, radiation cured or combinations thereof.Additional details on binder chemistry may be found in U.S. Pat. No.4,588,419 (Caul et al.), U.S. Pat. No. 4,751,138 (Tumey et al.), andU.S. Pat. No. 5,436,063 (Follett et al.), the disclosures of which areincorporated herein by reference.

More specifically with regard to vitrified bonded abrasives, vitreousbonding materials, which exhibit an amorphous structure and aretypically hard, are well known in the art. In some cases, the vitreousbonding material includes crystalline phases. Bonded, vitrified abrasivearticles according to the present invention may be in the shape of awheel (including cut off wheels), honing stone, mounted pointed or otherconventional bonded abrasive shape. A preferred vitrified bondedabrasive article according to the present invention is a grinding wheel.

Examples of metal oxides that are used to form vitreous bondingmaterials include: silica, silicates, alumina, soda, calcia, potassia,titania, iron oxide, zinc oxide, lithium oxide, magnesia, boria,aluminum silicate, borosilicate glass, lithium aluminum silicate,combinations thereof, and the like. Typically, vitreous bondingmaterials can be formed from composition comprising from 10 to 100%glass frit, although more typically the composition comprises 20% to 80%glass frit, or 30% to 70% glass frit. The remaining portion of thevitreous bonding material can be a non-frit material. Alternatively, thevitreous bond may be derived from a non-frit containing composition.Vitreous bonding materials are typically matured at a temperature(s) ina range of about 700° C. to about 1500° C., usually in a range of about800° C. to about 1300° C., sometimes in a range of about 900° C. toabout 1200° C., or even in a range of about 950° C. to about 1100° C.The actual temperature at which the bond is matured depends, forexample, on the particular bond chemistry.

Preferred vitrified bonding materials may include those comprisingsilica, alumina (desirably, at least 10 percent by weight alumina), andboria (desirably, at least 10 percent by weight boria). In most casesthe vitrified bonding material further comprise alkali metal oxide(s)(e.g., Na₂O and K₂O) (in some cases at least 10 percent by weight alkalimetal oxide(s)).

Binder materials may also contain filler materials or grinding aids,typically in the form of a particulate material. Typically, theparticulate materials are inorganic materials. Examples of usefulfillers for this invention include: metal carbonates (e.g., calciumcarbonate (e.g., chalk, calcite, marl, travertine, marble andlimestone), calcium magnesium carbonate, sodium carbonate, magnesiumcarbonate), silica (e.g., quartz, glass beads, glass bubbles and glassfibers) silicates (e.g., talc, clays, (montmorillonite) feldspar, mica,calcium silicate, calcium metasilicate, sodium aluminosilicate, sodiumsilicate) metal sulfates (e.g., calcium sulfate, barium sulfate, sodiumsulfate, aluminum sodium sulfate, aluminum sulfate), gypsum,vermiculite, wood flour, aluminum trihydrate, carbon black, metal oxides(e.g., calcium oxide (lime), aluminum oxide, titanium dioxide), andmetal sulfites (e.g., calcium sulfite).

In general, the addition of a grinding aid increases the useful life ofthe abrasive article. A grinding aid is a material that has asignificant effect on the chemical and physical processes of abrading,which results in improved performance. Although not wanting to be boundby theory, it is believed that a grinding aid(s) will (a) decrease thefriction between the abrasive particles and the workpiece being abraded,(b) prevent the abrasive particles from “capping” (i.e., prevent metalparticles from becoming welded to the tops of the abrasive particles),or at least reduce the tendency of abrasive particles to cap, (c)decrease the interface temperature between the abrasive particles andthe workpiece, or (d) decreases the grinding forces.

Grinding aids encompass a wide variety of different materials and can beinorganic or organic based. Examples of chemical groups of grinding aidsinclude waxes, organic halide compounds, halide salts and metals andtheir alloys. The organic halide compounds will typically break downduring abrading and release a halogen acid or a gaseous halide compound.Examples of such materials include chlorinated waxes liketetrachloronaphtalene, pentachloronaphthalene, and polyvinyl chloride.Examples of halide salts include sodium chloride, potassium cryolite,sodium cryolite, ammonium cryolite, potassium tetrafluoroboate, sodiumtetrafluoroborate, silicon fluorides, potassium chloride, and magnesiumchloride. Examples of metals include, tin, lead, bismuth, cobalt,antimony, cadmium, and iron titanium. Other miscellaneous grinding aidsinclude sulfur, organic sulfur compounds, graphite, and metallicsulfides. It is also within the scope of the present invention to use acombination of different grinding aids, and in some instances this mayproduce a synergistic effect. The preferred grinding aid is cryolite;the most preferred grinding aid is potassium tetrafluoroborate.

Grinding aids can be particularly useful in coated abrasive and bondedabrasive articles. In coated abrasive articles, grinding aid istypically used in the supersize coat, which is applied over the surfaceof the abrasive particles. Sometimes, however, the grinding aid is addedto the size coat. Typically, the amount of grinding aid incorporatedinto coated abrasive articles are about 50-300 g/m² (desirably, about80-160 g/m²). In vitrified bonded abrasive articles grinding aid istypically impregnated into the pores of the article.

The abrasive articles can contain 100% abrasive particles according tothe present invention, or blends of such abrasive particles with otherabrasive particles and/or diluent particles. However, at least about 2%by weight, desirably at least about 5% by weight, and more desirablyabout 30-100% by weight, of the abrasive particles in the abrasivearticles should be abrasive particles according to the presentinvention. In some instances, the abrasive particles according thepresent invention may be blended with another abrasive particles and/ordiluent particles at a ratio between 5 to 75% by weight, about 25 to 75%by weight about 40 to 60% by weight, or about 50% to 50% by weight(i.e., in equal amounts by weight). Examples of suitable conventionalabrasive particles include fused aluminum oxide (including white fusedalumina, heat-treated aluminum oxide and brown aluminum oxide), siliconcarbide, boron carbide, titanium carbide, diamond, cubic boron nitride,garnet, fused alumina-zirconia, and sol-gel-derived abrasive particles,and the like. The sol-gel-derived abrasive particles may be seeded ornon-seeded. Likewise, the sol-gel-derived abrasive particles may berandomly shaped or have a shape associated with them, such as a rod or atriangle. Examples of sol gel abrasive particles include those describedU.S. Pat. No. 4,314,827 (Leitheiser et al.), U.S. Pat. No. 4,518,397(Leitheiser et al.), U.S. Pat. No. 4,623,364 (Cottringer et al.), U.S.Pat. No. 4,744,802 (Schwabel), U.S. Pat. No. 4,770,671 (Monroe et al.),U.S. Pat. No. 4,881,951 (Wood et al.), U.S. Pat. No. 5,011,508 (Wald etal.), U.S. Pat. No. 5,090,968 (Pellow), U.S. Pat. No. 5,139,978 (Wood),U.S. Pat. No. 5,201,916 (Berg et al.), U.S. Pat. No. 5,227,104 (Bauer),U.S. Pat. No. 5,366,523 (Rowenhorst et al.), U.S. Pat. No. 5,429,647(Larmie), U.S. Pat. No. 5,498,269 (Larmie), and U.S. Pat. No. 5,551,963(Larmie), the disclosures of which are incorporated herein by reference.Additional details concerning sintered alumina abrasive particles madeby using alumina powders as a raw material source can also be found, forexample, in U.S. Pat. No. 5,259,147 (Falz), U.S. Pat. No. 5,593,467(Monroe), and U.S. Pat. No. 5,665,127 (Moltgen), the disclosures ofwhich are incorporated herein by reference. Additional detailsconcerning fused abrasive particles, can be found, for example, in U.S.Pat. No. 1,161,620 (Coulter), U.S. Pat. No. 1,192,709 (Tone), U.S. Pat.No. 1,247,337 (Saunders et al.), 1,268,533 (Allen), and U.S. Pat. No.2,424,645 (Baumann et al.), U.S. Pat. No. 3,891,408 (Rowse et al.), U.S.Pat. No 3,781,172 (Pett et al.), U.S. Pat. No. 3,893,826 (Quinan etal.), U.S. Pat. No. 4,126,429 (Watson), U.S. Pat. No. 4,457,767 (Poon etal.), U.S. Pat. No. 5,023,212 (Dubots et al.), U.S. Pat. No. 5,143,522(Gibson et al.), and U.S. Pat. No. 5,336,280 (Dubots et al.), andapplications having U.S. Ser. Nos. 09/495,978, 09/496,422, 09/496,638,and 09/496,713, each filed on Feb. 2, 2000, and, U.S. Ser. Nos.09/618,876, 09/618,879, 09/619,106, 09/619,191, 09/619,192, 09/619,215,09/619,289, 09/619,563, 09/619,729, 09/619,744, and 09/620,262, eachfiled on Jul. 19, 2000, and U.S. Ser. No. 09/772,730, filed Jan. 30,2001, the disclosures of which are incorporated herein by reference. Insome instances, blends of abrasive particles may result in an abrasivearticle that exhibits improved grinding performance in comparison withabrasive articles comprising 100% of either type of abrasive particle.

If there is a blend of abrasive particles, the abrasive particle typesforming the blend may be of the same size. Alternatively, the abrasiveparticle types may be of different particle sizes. For example, thelarger sized abrasive particles may be abrasive particles according tothe present invention, with the smaller sized particles being anotherabrasive particle type. Conversely, for example, the smaller sizedabrasive particles may be abrasive particles according to the presentinvention, with the larger sized particles being another abrasiveparticle type.

Examples of suitable diluent particles include marble, gypsum, flint,silica, iron oxide, aluminum silicate, glass (including glass bubblesand glass beads), alumina bubbles, alumina beads and diluentagglomerates. Abrasive particles according to the present invention canalso be combined in or with abrasive agglomerates. Abrasive agglomerateparticles typically comprise a plurality of abrasive particles, abinder, and optional additives. The binder may be organic and/orinorganic. Abrasive agglomerates may be randomly shape or have apredetermined shape associated with them. The shape may be a block,cylinder, pyramid, coin, square, or the like. Abrasive agglomerateparticles typically have particle sizes ranging from about 100 to about5000 micrometers, typically about 250 to about 2500 micrometers.Additional details regarding abrasive agglomerate particles may befound, for example, in U.S. Pat. No. 4,311,489 (Kressner), U.S. Pat. No.4,652,275 (Bloecher et al.), U.S. Pat. No. 4,799,939 (Bloecher et al.),U.S. Pat. No. 5,549,962 (Holmes et al.), and U.S. Pat. No. 5,975,988(Christianson), and applications having U.S. Ser. Nos. 09/688,444 and09/688,484, filed Oct. 16, 2001, the disclosures of which areincorporated herein by reference.

The abrasive particles may be uniformly distributed in the abrasivearticle or concentrated in selected areas or portions of the abrasivearticle. For example, in a coated abrasive, there may be two layers ofabrasive particles. The first layer comprises abrasive particles otherthan abrasive particles according to the present invention, and thesecond (outermost) layer comprises abrasive particles according to thepresent invention. Likewise in a bonded abrasive, there may be twodistinct sections of the grinding wheel. The outermost section maycomprise abrasive particles according to the present invention, whereasthe innermost section does not. Alternatively, abrasive particlesaccording to the present invention may be uniformly distributedthroughout the bonded abrasive article.

Further details regarding coated abrasive articles can be found, forexample, in U.S. Pat. No. 4,734,104 (Broberg), U.S. Pat. No. 4,737,163(Larkey), U.S. Pat. No. 5,203,884 (Buchanan et al.), U.S. Pat. No.5,152,917 (Pieper et al.), U.S. Pat. No. 5,378,251 (Culler et al.), U.S.Pat. No. 5,417,726 (Stout et al.), U.S. Pat. No. 5,436,063 (Follett etal.), U.S. Pat. No. 5,496,386 (Broberg et al.), U.S. Pat. No. 5, 609,706(Benedict et al.), U.S. Pat. No. 5,520,711 (Helmin), U.S. Pat. No.5,954,844 (Law et al.), U.S. Pat. No. 5,961,674 (Gagliardi et al.), andU.S. Pat. No. 5,975,988 (Christianson), the disclosures of which areincorporated herein by reference. Further details regarding bondedabrasive articles can be found, for example, in U.S. Pat. No. 4,543,107(Rue), U.S. Pat. No. 4,741,743 (Narayanan et al.), U.S. Pat. No.4,800,685 (Haynes et al.), U.S. Pat. No. 4,898,597 (Hay et al.), U.S.Pat. No. 4,997,461 (Markhoff-Matheny et al.), U.S. Pat. No. 5,037,453(Narayanan et al.), U.S. Pat. No. 5,110,332 (Narayanan et al.), and U.S.Pat. No. 5,863,308 (Qi et al.) the disclosures of which are incorporatedherein by reference. Further details regarding vitreous bonded abrasivescan be found, for example, in U.S. Pat. No. 4,543,107 (Rue), U.S. Pat.No. 4,898,597 (Hay et al.), U.S. Pat. No. 4,997,461 (Markhoff-Matheny etal.), U.S. Pat. No. 5,094,672 (Giles Jr. et al.), U.S. Pat. No.5,118,326 (Sheldon et al.), U.S. Pat. No. 5,131,926 (Sheldon et al.),U.S. Pat. No. 5,203,886 (Sheldon et al.), U.S. Pat. No. 5,282,875 (Woodet al.), U.S. Pat. No. 5,738,696 (Wu et al.), and U.S. Pat. No.5,863,308 (Qi), the disclosures of which are incorporated herein byreference. Further details regarding nonwoven abrasive articles can befound, for example, in U.S. Pat. No. 2,958,593 (Hoover et al.), thedisclosure of which is incorporated herein by reference.

The present invention provides a method of abrading a surface, themethod comprising contacting at least one abrasive particle according tothe present invention, with a surface of a workpiece; and moving atleast of one the abrasive particle or the contacted surface to abrade atleast a portion of said surface with the abrasive particle. Methods forabrading with abrasive particles according to the present inventionrange of snagging (i.e., high pressure high stock removal) to polishing(e.g., polishing medical implants with coated abrasive belts), whereinthe latter is typically done with finer grades (e.g., less ANSI 220 andfiner) of abrasive particles. The abrasive particle may also be used inprecision abrading applications, such as grinding cam shafts withvitrified bonded wheels. The size of the abrasive particles used for aparticular abrading application will be apparent to those skilled in theart.

Abrading with abrasive particles according to the present invention maybe done dry or wet. For wet abrading, the liquid may be introducedsupplied in the form of a light mist to complete flood. Examples ofcommonly used liquids include: water, water-soluble oil, organiclubricant, and emulsions. The liquid may serve to reduce the heatassociated with abrading and/or act as a lubricant. The liquid maycontain minor amounts of additives such as bactericide, antifoamingagents, and the like.

Abrasive particles according to the present invention may be used toabrade workpieces such as aluminum metal, carbon steels, mild steels,tool steels, stainless steel, hardened steel, titanium, glass, ceramics,wood, wood like materials, paint, painted surfaces, organic coatedsurfaces and the like. The applied force during abrading typicallyranges from about 1 to about 100 kilograms.

Advantages and embodiments of this invention are further illustrated bythe following examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention. All parts andpercentages are by weight unless otherwise indicated. Unless otherwisestated, all examples contained no significant amount of SiO₂, B₂O₃,P₂O₅, GeO₂, TeO₂, As₂O₃, and V₂O₅.

EXAMPLES Example 1

A polyethylene bottle was charged with 263.5 grams of alumina particles(obtained under the trade designation “APA-0.5” from Condea Vista,Tucson, Ariz.), 143.5 grams of yttrium oxide particles (obtained from H.C. Starck, Newton, Mass.), 93 grams of zirconium oxide particles (with anominal composition of 100 percent by weight (wt-%) ZrO₂ (+HfO₂);obtained under the trade designation “DK-2” from Zirconia Sales, Inc. ofMarietta, Ga.) and 300 grams of isopropyl alcohol. About 800 grams ofthe zirconia milling media (obtained from Tosoh Ceramics, Division ofBound Brook, N.J., under the trade designation “YTZ”) were added to thebottle, and the mixture was milled at 120 revolutions per minute (rpm)for 24 hours. After the milling, the milling media were removed and theslurry was poured onto a glass (“PYREX”) pan where it was dried using aheat-gun. The dried mixture was ground with a mortar and pestle andscreened through a 70-mesh screen (212-micrometer opening size screen).

After grinding and screening, some of the particles were fed into ahydrogen/oxygen torch flame. The torch used to melt the particles,thereby generating melted glass beads, was a Bethlehem bench burner PM2Dmodel B, obtained from Bethlehem Apparatus Co., Hellertown, Pa.,delivering hydrogen and oxygen at the following rates. For the innerring, the hydrogen flow rate was 8 standard liters per minute (SLPM) andthe oxygen flow rate was 3 SLPM. For the outer ring, the hydrogen flowrate was 23 (SLPM) and the oxygen flow rate was 9.8 SLPM. The dried andsized particles were fed directly into the torch flame, where they weremelted and transported to an inclined stainless steel surface(approximately 51 centimeters (cm) (20 inches) wide with the slope angleof 45 degrees) with cold water running over (approximately 8liters/minute) the surface to form beads.

About 50 grams of the resulting beads were placed in a graphite die andhot-pressed using a uniaxial pressing apparatus (obtained under thetrade designation “HP-50”, Thermal Technology Inc., Brea, Calif.). Thehot-pressing was carried out at 960° C. in an argon atmosphere and 13.8megapascals (MPa) (2000 pounds per square inch (2 ksi)) pressure. Theresulting hot-pressed disk was about 48 millimeters (mm) in diameter,and about 5 mm thick.

The hot-pressed disk was heat-treated in a furnace (an electricallyheated furnace (obtained under the trade designation “ModelKKSK-666-3100” from Keith Furnaces of Pico Rivera, Calif.)) as follows.The disk was first heated from room temperature (about 25° C.) to about900° C. at a rate of about 10° C./minutes and then held at 900° C. forabout 1 hour. Next, the disk was heated from about 900° C. to about1300° C. at a rate of about 10° C./minute and then held at 1300° C. forabout 1 hour, before cooling back to room temperature by turning off thefurnace.

FIG. 1 is a scanning electron microscope (SEM) photomicrograph of apolished section of hot-pressed and heat-treated Example 1 materialshowing the fine crystalline nature of the material. The polishedsection was prepared using conventional mounting and polishingtechniques. Polishing was done using a polisher (obtained from Buehlerof Lake Bluff, Ill. under the trade designation “ECOMET 3 TYPEPOLISHER-GRINDER”). The sample was polished for about 3 minutes with adiamond wheel, followed by three minutes of polishing with each of 45,30, 15, 9, and 3-micrometer diamond slurries. The polished sample wassputter coated with a thin layer of gold-palladium and viewed using JEOLSEM (Model JSM 840A).

The average microhardnesses of the material of this Example wasdetermined as follows. Loose beads (about 125 micrometers in size) weremounted in mounting resin (obtained under the trade designation “EPOMET”from Buehler Ltd., Lake Bluff, Ill.). The resulting cylinder of resinwas about 2.5 cm (1 inch) in diameter and about 1.9 cm (0.75 inch) tall.The mounted samples were polished using a conventional grinder/polisher(obtained under the trade designation “EPOMET” from Buehler Ltd.) andconventional diamond slurries with the final polishing step using a 1micrometer diamond slurry (obtained under the trade designation “METADI”from Buehler Ltd.) to obtain polished cross-sections of the sample.

The microhardness measurements were made using a conventionalmicrohardness tester (obtained under the trade designation “MITUTOYOMVK-VL” from Mitutoyo Corporation, Tokyo, Japan) fitted with a Vickersindenter using a 500-gram indent load. The microhardness measurementswere made according to the guidelines stated in ASTM Test Method E384Test Methods for Microhardness of Materials (1991), the disclosure ofwhich is incorporated herein by reference. The microhardness values werean average of 20 measurements. The average microhardness of the materialprior to heat treatment was about 8.5 GPa. The average microhardness ofthe material after heat-treatment (determined as described above exceptbeads were heat-treated at 1300° C. for 1 hour) was 15.9 GPa.

Examples 2-16

Examples 2-16 beads were prepared as described in Example 1, except theraw materials and the amounts of raw materials used are listed in Table1, below, and the milling of the raw materials was carried out in 90 mlof isopropyl alcohol with 200 grams of the ziconia media (obtained fromTosoh Ceramics, Division of Bound Brook, N.J., under the designation“YTZ”) at 120 rpm for 24 hours. The sources of the raw materials usedare listed in Table 2, below.

TABLE 1 Weight percent of Example components Batch amounts, g 2 Y₂O₃:28.08 Y₂O₃: 14.04 Al₂O₃: 58.48 Al₂O₃: 29.24 ZrO₂: 13.43 ZrO₂: 6.72 3Y₂O₃: 27.6 Y₂O₃: 13.8 Al₂O₃: 57.5 Al₂O₃: 23.75 ZrO₂: 14.9 ZrO₂: 7.45 4Y₂O₃: 27.44 Y₂O₃: 13.72 Al₂O₃: 57.14 Al₂O₃: 28.57 ZrO₂: 15.43 ZrO₂: 7.715 Y₂O₃: 28.7 Y₂O₃: 14.35 Al₂O₃: 55.7 Al₂O₃: 27.85 ZrO₂: 15.5 ZrO₂: 7.756 Y₂O₃: 19 Y₂O₃: 9.5 Al₂O₃: 51 Al₂O₃: 25.5 ZrO₂: 17.9 ZrO₂: 8.95 La₂O₃:12.1 La₂O₃: 6.05 7 Y₂O₃: 19.3 Y₂O₃: 9.65 Al₂O₃: 50.5 Al₂O₃: 25.25 ZrO₂:17.8 ZrO₂: 8.9 Nd₂O₃: 12.4 Nd₂O₃: 6.2 8 Y₂O₃: 19.1 Y₂O₃: 9.55 Al₂O₃: 50Al₂O₃: 25 ZrO₂: 17.8 ZrO₂: 8.9 Gd₂O₃: 13.1 Gd₂O₃: 6.55 9 Y₂O₃: 19.0Y₂O₃: 9.5 Al₂O₃: 49.7 Al₂O₃: 24.85 ZrO₂: 17.55 ZrO₂: 8.77 Er₂O₃: 13.8Er₂O₃: 6.9 10 Y₂O₃: 27.4 Y₂O₃: 13.7 Al₂O₃: 50.3 Al₂O₃: 25.15 ZrO₂: 17.8ZrO₂: 8.9 Li₂CO₃: 4.5 Li₂CO₃: 2.25 11 HfO₂: 20.08 HfO₂: 14.04 Al₂O₃:46.55 Al₂O₃: 23.27 Y₂O₃: 25.37 Y₂O₃: 12.67 12 Y₂O₃: 27.4 Y₂O₃: 13.7Al₂O₃: 50.3 Al₂O₃: 25.15 ZrO₂: 17.8 ZrO₂: 8.9 MgO: 4.5 MgO: 2.25 13Y₂O₃: 27.4 Y₂O₃: 13.7 Al₂O₃: 50.3 Al₂O₃: 25.15 ZrO₂: 17.8 ZrO₂: 8.9 CaO:4.5 CaO: 2.25 14 Y₂O₃: 27.4 Y₂O₃: 13.7 Al₂O₃: 50.3 Al₂O₃: 25.15 ZrO₂:17.8 ZrO₂: 8.9 TiO₂: 4.5 TiO₂: 2.25 15 Y₂O₃: 27.4 Y₂O₃: 13.7 Al₂O₃: 50.3Al₂O₃: 25.15 ZrO₂: 17.8 ZrO₂: 8.9 NaHCO₃: 2.25 NaHCO₃: 2.25 16 Y₂O₃:27.4 Y₂O₃: 13.7 Al₂O₃: 50.3 Al₂O₃: 25.15 ZrO₂: 17.8 ZrO₂: 8.9 SiO₂: 2.25SiO₂: 2.25

TABLE 2 Raw Material Source Alumina particles (Al₂O₃) Obtained fromCondea Vista, Tuscon, AZ under the trade designation “APA-0.5” Calciumoxide particles (CaO) Obtained from Alfa Aesar, Ward Hill, MA Hafniumoxide particles (HfO₂) Obtained from Teledyne Wah Chang Albany Company,Albany, OR Lanthanum oxide particles (La₂O₃) Obtained from MolycorpInc., Mountain Pass, CA Gadolinium oxide particles (Gd₂O₃) Obtained fromMolycorp Inc. Erbium oxide particles (Er₂O₃) Obtained from AldrichChemical Co., Milwaukee, WI Lithium carbonate particles (Li₂CO₃)Obtained from Aldrich Chemical Co. Magnesium oxide particles (MgO)Obtained from Aldrich Chemical Co. Neodymium oxide particles (Nd₂O₃)Obtained from Molycorp Inc. Silica particles (SiO₂) Obtained from AlfaAesar Sodium bicarbonate particles (NaHCO₃) Obtained from AldrichChemical Co. Titanium dioxide particles (TiO₂) Obtained from KemiraInc., Savannah, GA Yttria-stabilized zirconium oxide Obtained fromZirconia Sales, particles (Y-PSZ) Inc. of Marietta, GA under the tradedesignation “HSY-3”

Various properties/characteristics of some Example 2-16 materials weremeasured as follows. Powder X-ray diffraction (using an X-raydiffractometer (obtained under the trade designation “PHILLIPS XRG 3100”from Phillips, Mahwah, N.J) with copper K (1 radiation of 1.54050Angstrom) was used to qualitatively measure phases present in examplematerials. The presence of a broad diffused intensity peak was taken asan indication of the amorphous nature of a material. The existence ofboth a broad peak and well-defined peaks was taken as an indication ofexistence of crystalline matter within an amorphous matrix. Phasesdetected in various examples are reported in Table 3, below.

TABLE 3 Hot- Phases detected via T_(g), T_(x), pressing Example X-raydiffraction Color ° C. ° C. temp, ° C. 2 Amorphous* and Clear/milky 874932 980 Crystalline 3 Amorphous* and Clear/milky 871 934 — Crystalline 4Amorphous* and Clear/milky 874 937 — Crystalline 5 Amorphous* andClear/milky 870 942 — Crystalline 6 Amorphous* Clear 843 938 970 7Amorphous* Blue/pink 848 934 970 8 Amorphous* and Clear/milky 880 943Crystalline 9 Amorphous* and Pink 876 936 Crystalline 10 Amorphous*Clear 821 927 970 11 Amorphous* and Clear/ 867 948 — CrystallineGreenish 12 Amorphous* and Clear/milky 869 934 — Crystalline 13Amorphous* Clear 845 922 970 14 Amorphous* and Clear/milky 870 933Crystalline 15 Amorphous* Clear 831 916 970 16 Amorphous* Clear 826 926970

*Glass, as the example has a T_(g).

For differential thermal analysis (DTA), a material was screened toretain beads in the 90-125 micrometer size range. DTA runs were made(using an instrument obtained from Netzsch Instruments, Selb, Germanyunder the trade designation “NETZSCH STA 409 DTA/TGA”). The amount ofeach screened sample placed in a 100-microliter Al₂O₃ sample holder was400 milligrams. Each sample was heated in static air at a rate of 10°C./minute from room temperature (about 25° C.) to 1200° C.

Referring to FIG. 2, line 123 is the plotted DTA data for the Example 1material. Referring to FIG. 2 line 123, the material exhibited anendothermic event at a temperature around 875° C., as evidenced by thedownward curve of line 123. It was believed that this event was due tothe glass transition (T_(g)) of the material. At about 941° C., anexothermic event was observed as evidenced by the sharp peak in line123. It was believed that this event was due to the crystallization(T_(g)) of the material. These T_(g) and T_(x) values for other examplesare reported in Table 3, above.

The hot-pressing temperature at which appreciable glass flow occurred,as indicated by the displacement control unit of the hot pressingequipment described above, are reported for various examples in Table 3,above.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention, and it should be understood that thisinvention is not to be unduly limited to the illustrative embodimentsset forth herein.

1. Glass comprising Al₂O₃, Y₂O₃, and ZrO₂, wherein at least 80 percentby weight of the glass collectively comprises the Al₂O₃, Y₂O₃, and ZrO₂,and wherein the glass comprise at least 30 percent by weight Al₃O₃, atleast 20 percent by weight Y₂O₃, and ZrO₂ in a range from 15.43 to 30percent by weight, based on the total weight of the glass.
 2. Ceramiccomprising the glass according to claim
 1. 3. A method for making glasscomprising Al₂O₃, Y₂O₃, and ZrO₂, wherein at least 80 percent by weightof the glass collectively comprises the Al₂O₃, Y₂O₃, and ZrO₂, andwherein the glass comprise at least 30 percent by weight Al₂O₃, at least20 percent by weight Y₂O₃, and ZrO₂ in a range from 15.43 to 30 percentby weight, based on the total weight of the glass, the methodcomprising: melting sources of at least Al₂O₃, Y₂O₃, and ZrO₂ to providea melt; and cooling the melt to provide the glass.
 4. A method formaking ceramic comprising glass, wherein the class comprises Al₂O₃,Y₂O₃, and ZrO₂, wherein at least 80 percent by weight of the glasscollectively comprises the Al₂O₃, Y₂O₃, and ZrO₂, and wherein the glasscomprise at least 30 percent by weight Al₂O₃, at least 20 percent byweight Y₂O₃, and ZrO₂ in a range from 15.43 to 30 percent by weight,based on the total weight of the glass, the method comprising: meltingsources of at least Al₂O₃, Y₂O₃, and ZrO₂ to provide a melt; and coolingthe melt to provide the ceramic.
 5. A method for making an articlecomprising glass comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, wherein at least 80 percent by weight of the glass collectivelycomprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, based onthe total weight of the class the method comprising: melting at leastsources Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂ to provide a melt;cooling the melt to provide glass beads comprising glass comprisingAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 80percent by weight of the glass collectively comprises the Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂, based on the total weight of theglass, the glass having a T_(g); heating the glass beads above the T_(g)such that the glass beads coalesce to form a shape; and cooling thecoalesced shape to provide the article.
 6. A method for making anarticle comprising glass comprising Al₂O₃, Y₂O₃, and at least one ofZrO₂ or HfO₂, wherein at least 60 percent by weight of the glasscollectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, and less than 20 percent by weight SiO₂ and less than 20 percentby weight B₂O₃, based on the total weight of the glass, the methodcomprising: melting at least sources of Al₂O₃, Y₂O₃, and at least one ofZrO₂ or HfO₂ to provide a melt; cooling the melt to provide glass beadscomprising glass comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, wherein at least 60 percent by weight of the glass collectivelycomprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, and lessthan 20 percent by weight SiO₂ and less than 20 percent by weight B₂O₃,based on the total weight of the glass, the glass having a T_(g);heating the glass beads above the T_(g) such that the glass beadscoalesce to form a shape; and cooling the coalesced shape to provide thearticle.
 7. A method for making an article comprising glass comprisingAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60percent by weight of the glass collectively comprises the Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂, and less than 40 percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass, the method comprising: melting at least sources of Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂ to provide a melt; cooling the melt toprovide glass beads comprising glass comprising Al₂O₃, Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 60 percent by weight of theglass collectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂or HfO₂, and less than 40 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass, the glass having a T_(g);heating the glass beads above the T_(g) such that the glass beadscoalesce to form a shape; and cooling the coalesced shape to provide thearticle.
 8. A method for making an article comprising glass comprisingAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 80percent by weight of the glass collectively comprises the Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂, based on the total weight of theglass, the method comprising: melting at least sources of Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂ to provide a melt; cooling the melt toprovide glass beads comprising glass comprising Al₂O₃, Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 80 percent by weight of theglass collectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂or HfO₂, based on the total weight of the glass, the glass having aT_(g); converting the glass beads to provide glass powder; heating theglass powder above the T_(g) such that the glass powder coalesces toform a shape; and cooling the coalesced shape to provide the article. 9.A method for making an article comprising glass comprising Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂, wherein at least 60 percent by weightof the glass collectively comprises the Al₂O₃, Y₂O₃, and at least one ofZrO₂ or HfO₂, and less than 20 percent by weight SiO₂ and less than 20percent by weight B₂O₃, based on the total weight of the glass, themethod comprising: melting at least sources of Al₂O₃, Y₂O₃, and at leastone of ZrO₂ or HfO₂ to provide a melt; cooling the melt to provide glassbeads comprising glass comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass collectivelycomprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, and lessthan 20 percent by weight SiO₂ and less than 20 percent by weight B₂O₃,based on the total weight of the glass, the glass having a T_(g);converting the glass beads to provide glass powder; heating the glasspowder above the T_(g) such that the glass powder coalesces to form ashape; and cooling the coalesced shape to provide the article.
 10. Amethod for making an article comprising glass comprising Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂, wherein at least 60 percent by weightof the glass collectively comprises the Al₂O₃, Y₂O₃, and at least one ofZrO₂ or HfO₂, and less than 40 percent by weight collectively SiO₂,B₂O₃, and P₂O₅, based on the total weight of the glass, the methodcomprising: melting at least sources of Al₂O₃, Y₂O₃, and at least one ofZrO₂ or HfO₂ to provide a melt; cooling the melt to provide glass beadscomprising glass comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, wherein at least 60 percent by weight of the glass collectivelycomprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, and lessthan 40 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based onthe total weight of the glass, the glass having a T_(g); converting theglass beads to provide glass powder; heating the glass powder above theT_(g) such that the glass powder coalesces to form a shape; and coolingthe coalesced shape to provide the article.
 11. Ceramic comprising atleast 75 percent by volume glass, the glass comprising Al₂O₃, Y₂O₃, andZrO₂, wherein at least 80 percent by weight of the glass collectivelycomprises the Al₂O₃, Y₂O₃, and ZrO₂, and wherein the glass comprise atleast 30 percent by weight Al₂O₃, at least 20 percent by weight Y₂O₃,and ZrO₂ in a range from 15.43 to 30 percent by weight, based on thetotal weight of the glass.
 12. Glass-ceramic comprising Al₂O₃, Y₂O₃, andat least one of ZrO₂ or HfO₂, wherein at least 80 percent by weight ofthe glass-ceramic collectively comprises the Al₂O₃, Y₂O₃, and at leastone of ZrO₂ or HfO₂, based on the total weight of the glass-ceramic. 13.The glass-ceramic according to claim 12 collectively comprising at least80 percent by weight of the Al₂O₃, Y₂O₃, and ZrO₂, based on the totalweight of the glass-ceramic.
 14. Glass-ceramic comprising Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂, wherein at least 60 percent by weightof the glass-ceramic collectively comprises the Al₂O₃, Y₂O₃, and atleast one of ZrO₂ or HfO₂, and less than 20 percent by weight SiO₂ andless than 20 percent by weight B₂O₃, based on the total weight of theglass-ceramic.
 15. The glass-ceramic according to claim 14 collectivelycomprising at least 60 percent by weight of the Al₂O₃, Y₂O₃, and ZrO₂,based on the total weight of the glass-ceramic.
 16. Glass-ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 60 percent by weight of the glass-ceramic collectively comprisesthe Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, and less than 40percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based on the totalweight of the glass-ceramic.
 17. The glass-ceramic according to claim 16collectively comprising at least 60 percent by weight of the Al₂O₃,Y₂O₃, and ZrO₂, based on the total weight of the glass-ceramic.
 18. Amethod for making glass-ceramic comprising Al₂O₃, Y₂O₃, and at least oneof ZrO₂ or HfO₂, wherein at least 80 percent by weight of theglass-ceramic collectively comprises the Al₂O₃, Y₂O₃, and at least oneof ZrO₂ or HfO₂, based on the total weight of the glass-ceramic, themethod comprising: heat-treating glass comprising Al₂O₃, Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 80 percent by weight of theglass collectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂or HfO₂, based on the total weight of the glass to provide theglass-ceramic.
 19. A method for making glass-ceramic comprising Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 80 percent byweight of the glass-ceramic collectively comprises the Al₂O₃, Y₂O₃, andat least one of ZrO₂ or HfO₂, based on the total weight of theglass-ceramic, the method comprising: heat-treating ceramic comprisingglass, wherein the glass comprises Al₂O₃, Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 80 percent by weight of the glass collectivelycomprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, based onthe total weight of the glass to provide the glass-ceramic.
 20. A methodfor making glass-ceramic comprising Al₂O₃, Y₂O₃, and at least one ofZrO₂ or HfO₂, wherein at least 60 percent by weight of the glass-ceramiccollectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, and less than 20 percent by weight SiO₂ and less than 20 percentby weight B₂O₃, based on the total weight of the glass-ceramic, themethod comprising: heat-treating glass comprising Al₂O₃, Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 60 percent by weight of theglass collectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂or HfO₂, and less than 20 percent by weight SiO₂ and less than 20percent by weight B₂O₃, based on the total weight of the glass toprovide the glass-ceramic.
 21. A method for making glass-ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 60 percent by weight of the glass-ceramic collectively comprisesthe Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, and less than 20percent by weight SiO₂ and less than 20 percent by weight B₂O₃, based onthe total weight of the glass-ceramic, the method comprising:heat-treating ceramic comprising glass, wherein the glass comprisesAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60percent by weight of the glass collectively comprises the Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂, and less than 20 percent by weightSiO₂ and less than 20 percent by weight B₂O₃, based on the total weightof the glass to provide the glass-ceramic.
 22. A method for makingglass-ceramic comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂,wherein at least 60 percent by weight of the glass-ceramic collectivelycomprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, and lessthan 40 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based onthe total weight of the glass-ceramic, the method comprising:heat-treating glass comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, wherein at least 60 percent by weight of the glass collectivelycomprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, and lessthan 40 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based onthe total weight of the glass to provide the glass-ceramic.
 23. A methodfor making glass-ceramic comprising Al₂O₃, Y₂O₃, and at least one ofZrO₂ or HfO₂, wherein at least 60 percent by weight of the glass-ceramiccollectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, and less than 40 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass-ceramic, the methodcomprising: heat-treating ceramic comprising glass, wherein the glasscomprises Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 60 percent by weight of the glass collectively comprises theAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, and less than 40 percentby weight collectively SiO₂, B₂O₃, and P₂O₅, based on the total weightof the glass to provide the glass-ceramic.
 24. A method for makingglass-ceramic comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂,the method comprising: heat-treating glass comprising Al₂O₃, Y₂O₃, andat least one of ZrO₂ or HfO₂ to provide the glass-ceramic, wherein theglass-ceramic (a) exhibits a microstructure comprising crystalliteshaving an average crystallite size of less than 1 micrometer, and (b) isfree of eutectic microstructure features.
 25. A method for makingglass-ceramic comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂,the method comprising: heat-treating ceramic comprising glass, whereinthe glass comprises Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂ toprovide the glass-ceramic wherein the glass-ceramic (a) exhibits amicrostructure comprising crystallites having an average crystallitesize of less than 1 micrometer, and (b) is free of eutecticmicrostructure features.
 26. A method for making a glass-ceramicarticle, the method comprising: converting glass to provide glasspowder, the glass comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, wherein at least 80 percent by weight of the glass collectivelycomprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, based onthe total weight of the glass, the glass having a T_(g); heating theglass powder above the T_(g) such that the glass powder coalesces toform a shape; cooling the coalesced shape to provide a glass article;and heat-treating the glass article to provide a glass-ceramic article.27. A method for making a glass-ceramic article, the method comprising:converting glass to provide glass powder, the glass comprising Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60 percent byweight of the glass collectively comprises the Al₂O₃, Y₂O₃, and at leastone of ZrO₂ or HfO₂, and less than 20 percent by weight SiO₂ and lessthan 20 percent by weight B₂O₃, based on the total weight of the glass,the glass having a T_(g); heating the glass powder above the T_(g) suchthat the glass powder coalesces to form a shape; cooling the coalescedshape to provide a glass article; and heat-treating the glass article toprovide a glass-ceramic article.
 28. A method for making a glass-ceramicarticle, the method comprising: converting glass to provide glasspowder, the glass comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, wherein at least 60 percent by weight of the glass collectivelycomprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, and lessthan 40 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based onthe total weight of the glass, the glass having a T_(g); heating theglass powder above the T_(g) such that the glass powder coalesces toform a shape; cooling the coalesced shape to provide a glass article;and heat-treating the glass article to provide a glass-ceramic article.29. Glass-ceramic comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, wherein the glass-ceramic (a) exhibits a microstructure comprisingcrystallites having an average crystallite size of less than 200nanometers and (b) has a density of at least 90% of theoretical density.30. Glass-ceramic comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, wherein the glass-ceramic (a) exhibits a microstructure comprisingcrystallites, wherein none of the crystallites are greater than 200nanometers in size and (b) has a density of at least 90% of theoreticaldensity.
 31. Glass-ceramic comprising Al₂O₃, Y₂O₃, and at least one ofZrO₂ or HfO₂, wherein the glass-ceramic (a) exhibits a microstructurecomprising crystallites, wherein at least a portion of the crystallitesare not greater than 150 nanometers in size and (b) has a density of atleast 90% of theoretical density.
 32. Ceramic comprising at least 75percent by volume glass-ceramic, the glass-ceramic comprising Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein the ceramic (a) exhibitsa microstructure comprising crystallites having an average crystallitesize of less than 200 nanometers and (b) has a density of at least 90%of theoretical density.
 33. Ceramic comprising at least 75 percent byvolume glass-ceramic, the glass-ceramic comprising Al₂O₃, Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein the ceramic (a) exhibits amicrostructure comprising crystallites, wherein none of the crystallitesare greater than 200 nanometers in size and (b) has a density of atleast 90% of theoretical density.
 34. Ceramic comprising at least 75percent by volume glass-ceramic, the glass-ceramic comprising Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein the ceramic (a) exhibitsa microstructure comprising crystallites, wherein at least a portion ofthe crystallites are not greater than 150 nanometers in size and (b) hasa density of at least 90% of theoretical density.
 35. Ceramic comprisingat least 75 percent by volume glass-ceramic, the glass-ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein theceramic (a) exhibits a microstructure comprising crystallites having anaverage crystallite size not greater than 200 nanometer, in size and (b)has a density of at least 90% of theoretical density.
 36. The ceramicaccording to claim 35 wherein the glass-ceramic comprising Al₂O₃, Y₂O₃,and ZrO₂.
 37. Abrasive particle comprising a glass-ceramic comprisingAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 80percent by weight of the glass-ceramic collectively comprises the Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, based on the total weight of theglass-ceramic.
 38. Abrasive particle comprising a glass-ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 60 percent by weight of the glass-ceramic collectively comprisesthe Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, and less than 20percent by weight SiO₂ and less than 20 percent by weight B₂O₃, based onthe total weight of the glass-ceramic.
 39. Abrasive particle comprisinga glass-ceramic comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, wherein at least 60 percent by weight of the glass-ceramiccollectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, and less than 40 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass-ceramic.
 40. A method formaking abrasive particles, the method comprising: heat-treating glassparticles comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂,wherein at least 80 percent by weight of the glass collectivelycomprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, based onthe total weight of the glass particles, to provide glass-ceramicabrasive particles.
 41. A method for making abrasive particles, themethod comprising: heat-treating particles comprising glass, wherein theglass comprises Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, whereinat least 80 percent by weight of the glass collectively comprises theAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, based on the total weightof the glass particles, to provide glass-ceramic abrasive particles. 42.A method for making abrasive particles, the method comprising:heat-treating glass comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, wherein at least 80 percent by weight of the glass collectivelycomprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, based onthe total weight of the glass, to provide glass-ceramic; and convertingthe glass-ceramic to provide abrasive particles.
 43. A method for makingabrasive particles, the method comprising: heat-treating ceramiccomprising glass, wherein the glass comprises Al₂O₃, Y₂O₃, and at leastone of ZrO₂ or HfO₂, wherein at least 80 percent by weight of the glasscollectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, based on the total weight of the glass, to provide glass-ceramic;and converting the glass-ceramic to provide abrasive particles.
 44. Amethod for making abrasive particles, the method comprising:heat-treating glass particles comprising Al₂O₃, Y₂O₃, and at least oneof ZrO₂ or HfO₂, wherein at least 60 percent by weight of the glasscollectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, and less than 20 percent by weight SiO₂ and less than 20 percentby weight B₂O₃, based on the total weight of the glass particles, toprovide glass-ceramic abrasive particles.
 45. A method for makingabrasive particles, the method comprising: heat-treating particlescomprising glass, wherein the glass comprises Al₂O₃, Y₂O₃, and at leastone of ZrO₂ or HfO₂, wherein at least 60 percent by weight of the glasscollectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, and less than 20 percent by weight SiO₂ and less than 20 percentby weight B₂O₃, based on the total weight of the glass particles, toprovide glass-ceramic abrasive particles.
 46. A method for makingabrasive particles, the method comprising: heat-treating glasscomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein atleast 60 percent by weight of the glass collectively comprises theAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, and less than 20 percentby weight SiO₂ and less than 20 percent by weight B₂O₃, based on thetotal weight of the glass, to provide glass-ceramic; and converting theglass-ceramic to provide abrasive particles.
 47. A method for makingabrasive particles, the method comprising: heat-treating ceramiccomprising glass, wherein the glass comprises Al₂O₃, Y₂O₃, and at leastone of ZrO₂ or HfO₂, wherein at least 60 percent by weight of the glasscollectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ orHfO₂, and less than 20 percent by weight SiO₂ and less than 20 percentby weight B₂O₃, based on the total weight of the glass, to provideglass-ceramic; and converting the glass-ceramic to provide abrasiveparticles.
 48. A method for making abrasive particles, the methodcomprising: heat-treating glass particles comprising Al₂O₃, Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 60 percent by weight of theglass collectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂or HfO₂, and less than 40 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass particles, to provideglass-ceramic abrasive particles.
 49. A method for making abrasiveparticles, the method comprising: heat-treating particles comprisingglass, wherein the glass comprises Al₂O₃, Y₂O₃, and at least one of ZrO₂or HfO₂, wherein at least 60 percent by weight of the glass collectivelycomprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, and lessthan 40 percent by weight collectively SiO₂, B₂O₃, and P₂O₅, based onthe total weight of the glass particles, to provide glass-ceramicabrasive particles.
 50. A method for making abrasive particles, themethod comprising: heat-treating glass comprising Al₂O₃, Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 60 percent by weight of theglass collectively comprises the Al₂O₃, Y₂O₃, and at least one of ZrO₂or HfO₂, and less than 40 percent by weight collectively SiO₂, B₂O₃, andP₂O₅, based on the total weight of the glass, to provide glass-ceramic;and converting the glass-ceramic to provide abrasive particles.
 51. Amethod for making abrasive particles, the method comprising:heat-treating ceramic comprising glass, wherein the glass comprisesAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 60percent by weight of the glass collectively comprises the Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂, and less than 40 percent by weightcollectively SiO₂, B₂O₃, and P₂O₅, based on the total weight of theglass, to provide glass-ceramic; and converting the glass-ceramic toprovide abrasive particles.
 52. A method for making abrasive particles,the method comprising: heat-treating glass particles comprising Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂ to provide the glass-ceramicabrasive particles, wherein the glass-ceramic (a) exhibits amicrostructure comprising crystallites having an average crystallitesize of less than 1 micrometer, and (b) is free of eutecticmicrostructure features.
 53. A method for making abrasive particles, themethod comprising: heat-treating particles comprising glass, wherein theglass comprises Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂ to providethe glass-ceramic abrasive particles, wherein the glass-ceramic (a)exhibits a microstructure comprising crystallites having an averagecrystallite size of less than 1 micrometer, and (b) is free of eutecticmicrostructure features.
 54. A method for making abrasive particles, themethod comprising: heat-treating glass comprising Al₂O₃, Y₂O₃, and atleast one of ZrO₂ or HfO₂ to provide the glass-ceramic, wherein theglass-ceramic (a) exhibits a microstructure comprising crystalliteshaving an average crystallite size of less than 1 micrometer, and (b) isfree of eutectic microstructure features; and converting theglass-ceramic to provide abrasive particles.
 55. A method for makingabrasive particles, the method comprising: heat-treating ceramiccomprising glass, wherein the glass comprises Al₂O₃, Y₂O₃, and at leastone of ZrO₂ or HfO₂ to provide the glass-ceramic, wherein theglass-ceramic (a) exhibits a microstructure comprising crystalliteshaving an average crystallite size of less than 1 micrometer, and (b) isfree of eutectic microstructure features; and converting theglass-ceramic to provide abrasive particles.
 56. Abrasive particlecomprising a glass-ceramic comprising Al₂O₃, Y₂O₃, and at least one ofZrO₂ or HfO₂, wherein the glass-ceramic (a) exhibits a microstructurecomprising crystallites having an average crystallite size of less than200 nanometers and (b) a density of at least 90% of theoretical density.57. The abrasive particle according to claim 56 comprising at least 90percent by volume of said ceramic, based on the total volume of saidabrasive particle.
 58. Abrasive particle comprising a glass-ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein theglass-ceramic (a) exhibits a microstructure comprising crystallites,wherein none of the crystallites are greater than 200 nanometers in sizeand (b) a density of at least 90% of theoretical density.
 59. Theabrasive particle according to claim 58 comprising at least 90 percentby volume of said ceramic, based on the total volume of said abrasiveparticle.
 60. Abrasive particle comprising a glass-ceramic comprisingAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein the glass-ceramic(a) exhibits a microstructure comprising crystallites, wherein at leasta portion of the crystallites are not greater than 150 nanometers insize and (b) a density of at least 90% of theoretical density.
 61. Theabrasive particle according to claim 60 comprising at least 90 percentby volume of said ceramic, based on the total volume of said abrasiveparticle.
 62. Abrasive particle comprising ceramic comprising at least75 percent by volume glass-ceramic, the glass-ceramic comprising Al₂O₃,Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein the ceramic (a) exhibitsa microstructure comprising crystallites having an average crystallitesize of less than 200 nanometer, and (b) a density of at least 90% oftheoretical density.
 63. The abrasive particle according to claim 62comprising at least 90 percent by volume of said ceramic, based on thetotal volume of said abrasive particle.
 64. Abrasive particle comprisingceramic comprising at least 75 percent by volume glass-ceramic theglass-ceramic comprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂,wherein the ceramic (a) exhibits a microstructure comprisingcrystallites, wherein none of the crystallites are greater than 200nanometers in size and (b) a density of at least 90% of theoreticaldensity.
 65. The abrasive particle according to claim 64 comprising atleast 90 percent by volume of said ceramic, based on the total volume ofsaid abrasive particle.
 66. Abrasive particle comprising ceramiccomprising at least 75 percent by volume glass-ceramic the glass-ceramiccomprising Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein theceramic (a) exhibits a microstructure comprising crystallites, whereinat least a portion of the crystallites are greater than 150 nanometersin size and (b) a density of at least 90% of theoretical density. 67.The abrasive particle according to claim 66 comprising at least 90percent by volume of said ceramic, based on the total volume of saidabrasive particle.
 68. Abrasive particle comprising ceramic comprisingat least 75 percent by volume glass-ceramic the glass-ceramic comprisingAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein the ceramic (a)exhibits a microstructure comprising crystallites having an averagecrystallite size not greater than 200 nanometers in size and (b) adensity of at least 90% of theoretical density.
 69. The abrasiveparticle according to claim 68 comprising at least 90 percent by volumeof said ceramic, based on the total volume of said abrasive particle.70. A plurality of abrasive particles having a specified nominal grade,wherein at least a portion of the plurality of abrasive particlescomprise alpha Al₂O₃, crystalline ZrO₂, and a first complex Al₂O₃.Y₂O₃,wherein at least one of the alpha Al₂O₃, the crystalline ZrO₂, or thefirst complex Al₂O₃.Y₂O₃ has an average crystal size not greater than150 nanometers, and wherein the abrasive particles of the portion have adensity of at least 90 percent of theoretical density.
 71. An abrasivearticle comprising a binder and a plurality of abrasive particles,wherein at least a portion of the abrasive particles comprise alphaAl₂O₃, crystalline ZrO₂, and a first complex Al₂O₃.Y₂O₃, and wherein atleast one of the alpha Al₂O₃, the crystalline ZrO₂, or the first complexAl₂O₃.Y₂O₃ has an average crystal size not greater than 150 nanometers,and wherein the abrasive particles of the portion have a density of atleast 90 percent of theoretical density.
 72. A method of abrading asurface, the method comprising: providing an abrasive article comprisinga binder and a plurality of abrasive particles, wherein at least aportion of the abrasive particles comprise alpha Al₂O₃, crystallineZrO₂, and a first complex Al₂O₃.Y₂O₃, wherein at least one of the alphaAl₂O₃, the crystalline ZrO₂, or the first complex Al₂O₃.Y₂O₃ has anaverage crystal size not greater than 150 nanometers, and wherein theabrasive particles of the portion have a density of at least 90 percentof theoretical density; contacting at least one of the abrasiveparticles comprising the alpha Al₂O₃, the crystalline ZrO₂, and thefirst complex Al₂O₃.Y₂O₃ with a surface of a workpiece; and moving atleast one of the contacted abrasive particles comprising the alphaAl₂O₃, the crystalline ZrO₂, and the first complex Al₂O₃.Y₂O₃ or thecontacted surface to abrade at least a portion of the surface with thecontacted abrasive particle comprising the alpha Al₂O₃, the crystallineZrO₂, and the first complex Al₂O₃.Y₂O₃.
 73. A plurality of abrasiveparticles having a specified nominal grade, wherein at least a portionof the plurality of abrasive particles comprise a first complexAl₂O₃.Y₂O₃, a second, different complex Al₂O₃.Y₂O₃, and crystallineZrO₂, wherein for at least one of the first complex Al₂O₃.Y₂O₃, thesecond complex Al₂O₃.Y₂O₃, or the crystalline ZrO₂, at least 90 percentby number of the crystal sizes thereof are not greater than 200nanometers, and wherein the abrasive particles of the portion have adensity of at least 90 percent of theoretical density.
 74. An abrasivearticle comprising a binder and a plurality of abrasive particles,wherein at least a portion of the abrasive particles comprise a firstcomplex Al₂O₃.Y₂O₃, a second, different complex Al₂O₃.Y₂O₃, andcrystalline ZrO₂, wherein in such portion, for at least one of the firstcomplex Al₂O₃.Y₂O₃, the second complex Al₂O₃.Y₂O₃, or the crystallineZrO₂, at least 90 percent by number of the crystal sizes thereof are notgreater than 200 nanometers, and wherein the abrasive particles of theportion have a density of at least 90 percent of theoretical density.75. A method of abrading a surface, the method comprising: providing anabrasive article comprising a binder and a plurality of abrasiveparticles, wherein at least a portion of the abrasive particles comprisea first complex Al₂O₃.Y₂O₃, a second, different complex Al₂O₃.Y₂O₃, andcrystalline ZrO₂, wherein in such portion, for at least one of the firstcomplex Al₂O₃.Y₂O₃, the second complex Al₂O₃.Y₂O₃, or the crystallineZrO₂, at least 90 percent by number of the crystal sizes thereof are notgreater than 200 nanometers, and wherein the abrasive particles of theportion have a density of at least 90 percent of theoretical density;contacting at least one of the abrasive particles comprising the firstcomplex Al₂O₃.Y₂O₃, the second complex Al₂O₃.Y₂O₃, and the crystallineZrO₂ with a surface of a workpiece; and moving at least one of thecontacted abrasive particles comprising the first complex Al₂O₃.Y₂O₃,the second complex Al₂O₃.Y₂O₃, and the crystalline ZrO₂ or the contactedsurface to abrade at least a portion of the surface with the contactedabrasive particle comprising the first complex Al₂O₃.Y₂O₃, the secondcomplex Al₂O₃.Y₂O₃, and the crystalline ZrO₂.
 76. Glass comprisingAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 80percent by weight of the glass collectively comprises the Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂, based on the total weight of theglass, wherein the glass has x, y, and z dimensions each perpendicularto each other, and wherein each of the x, y, and z dimensions is atleast 5 mm.
 77. The glass according to claim 76 collectively comprisingat least 80 percent by weight of the Al₂O₃, Y₂O₃, and ZrO₂, based on thetotal weight of the glass.
 78. Ceramic comprising the glass aecordine toclaim
 76. 79. A method for making glass comprising Al₂O₃, Y₂O₃, and atleast one of ZrO₂ or HfO₂, wherein at least 80 percent by weight glasscollectively comprises the Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂,based on the total weight of the glass, the method comprising: meltingsources of at least Al₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂ toprovide a melt; and cooling the melt to provide the glass, wherein theglass has x, y, and z dimensions each perpendicular to each other, andwherein each of the x, y, and z dimensions is at least 5 mm.
 80. Amethod for making ceramic comprising glass, wherein the glass comprisesAl₂O₃, Y₂O₃, and at least one of ZrO₂ or HfO₂, wherein at least 80percent by weight of the glass collectively comprises the Al₂O₃, Y₂O₃,and at least one of ZrO₂ or HfO₂, based on the total weight of theglass, wherein class has x, y, and z dimensions each perpendicular toeach other, and wherein each of the x, y, and z dimensions is at least 5mm the method comprising: melting sources of at least Al₂O₃, Y₂O₃, andat least one of ZrO₂ or HfO₂ to provide a melt; and cooling the melt toprovide the ceramic.